If you want a sure thing, you should head over to Utgarde Pinnacle and get Vengeance Be Mine!, the quest to kill King Ymiron. You can do this on Heroic or Normal modes and be rewarded with the Faceguard of Punishment, which gives a whopping 68 Hit Rating. If you're up to facing Loken in heroic Halls of Lightning, however, the Planetary Helm is a better option with better stats overall but slightly less Hit.
If you don't want to head to an instance but have Gold to spare, the world drop Skullcage of Eternal Terror gives decent Hit and a hefty amount of Crit, too. Of course, since you're in a spending mood, why not get a Blacksmith to craft you a Spiked Titansteel Helm? It's stats will change in Patch 3.0.8, losing Agility and gaining Critical Strike rating as well as a blue socket. While somewhat pricey, helms are one of the harder pieces to replace in a raid and this should last you well into your 25-mans.
The shoulders are generally the most difficult item to upgrade into epics, as the only epic shoulders are Tier 7 pieces, zone drops from Naxxramas, and Arena gear with ratings requirements. Until then, you'll have to settle for a pretty decent blue, the Pauldrons of the Lightning Revenant, which drop off Ionar in normal Halls of Lightning. You won't really need the +Stamina socket bonus but you're going to get it anyway, as it's a red slot perfect for a Bold gem.
If you're unlucky with drops, make sure to pick up Diametrically Opposed going into the Halls of Lightning. The quest requires you to kill Volkhan and rewards the Mantle of Volkhan. As you can see, a trip to the Halls of Lightning is pretty much worth it for Retribution Paladins.
Since the Tier 7 chest has no Hit rating, you'll do well to look and be satisfied with blues in the chest slot for the meantime. Novos the Summoner in heroic Drak'tharon Keep drops the Breastplate of Undeath while Eck the Ferocious in heroic Gundrak drops the Engraved Chestplate of Eck. The latter wins out slightly due to having more Hit as well as two sockets. If you're not yet ready for heroics -- but really, who isn't? -- you can hit normal Oculus and hope Varos Cloudstrider drops the Wing Commander's Breastplate.
You know why Halls of Lightning is so awesome? No, it's not because of Loken. It's because it's sort of the one-stop-shop for melee DPS plate with Hit. Take The General's Steel Girdle, for example. It drops off General Bjarngrim, the instance's first boss. Barring heroics, you can give the Culling of Stratholme a shot where Salramm the Fleshcrafter drops Spiked Metal Clice.
The legs slot is one of the easiest to upgrade with a Hit piece and will likely be the one slot which you'll get most of your +Hit from. The ultimate goal pre-Naxxramas should be the Staggering Legplates from heroic Utgarde Keep, arguably the easiest heroic in the game. With two sockets, a massive +80 Hit, these epic pants will serve any Retadin well into the 25-mans and perhaps even until Ulduar. Even Tier 7 legs are a mere sidegrade, with 80 Hit Rating freeing up a lot of points in other slots.
Varos Cloudstrider in heroic Oculus has a pair of blue legplates that aren't too shabby, either. The Legplates of the Oculus Guardian don't have sockets but has decent stats overall, some Agility, and a nearly-as-massive 77 Hit Rating. Lastly, anyone who has leveled in Dragonblight -- and you should, really -- will be picking up the Warchief's or Wrynn's Legplates of Carnage from the supremely epic questline that leads to The Battle for the Undercity.
Not too many great +Hit plate for the feet, but there are options. The Berserker's Sabatons are a zone drop from Utgarde Pinnacle, so some might luck out while doing the place. The Auction House might be a better place to hope for it, though, although I wouldn't recommend shelling out the Gold unless you're starved for Hit. Alternatively, you can pick up Trollkickers from doing One of a Kind in Gundrak. Still, the Hit on these plate pieces aren't so high that you should go out of your way for them.
The wrist slots are also better served with pure Strength items and other stats, but it's easy enough to put something there with Hit. Blacksmiths can craft Vengeance Bindings with only twelve Saronite Bars and an Eternal Fire, so why not? Cast Iron Shackles are a world drop BoE that you might chance upon at the Auction House. Just like the boots, if you don't have +Hit in this slot, don't sweat it, specially if you have high numbers elsewhere.
On the other hand, the hand slot has an excellent piece in the Cache of Eregos in heroic Oculus. The Gauntlets of Dragon Wrath are the best gloves a Retribution Paladin can get pre-raids, and will probably serve you well into Naxxramas. There are also the Gauntlets of the Culling which you'll receive the very first time you do the Culling of Stratholme, in the quest to accompany Arthas as he does his dastardly deeds. It's not epic, but it's a whopping +50 Hit.
You just can't go wrong with a 2-hander with enough top-end and +Hit to boot. This makes investing in a Titansteel Destroyer worth it, as it makes any drop from normal Naxxramas a sidegrade. I can't recommend anything less because as Retribution Paladins, our weapons make up a large part of our DPS, so getting the bigger, badder weapon is key. If you simply don't have the cash for this, though, there's the perfectly free Dreadlord's Blade after you scare off Mal'ganis in the Culling of Stratholme.
It's important to note that getting all of these pieces will push you way past the Hit cap, which will end up hurting your DPS instead of helping it. 262.4 is also the cap you'll need for raids -- it is too much for heroics and more so in PvP, where you'll need even less. It's key to hit the cap if you want to consider yourself raid-ready and optimize your DPS. Ideally, you can pick up all the epic items on the list, which pushes your Hit to 232, making you completely competitive for heroics and even graduate from them. After capping your Hit, concentrate on stacking as much Strength as possible and worry about the other stats later. Have fun!