One of the weirdest changes in Northrend so far is the way First Aid training works, strangely enough. Used to be that once you hit a certain level, you could just go run to the trainer to train up the next wave of bandages (or you could buy a manual from a trainer somewhere), but not so in the expansion: to get Heavy Frostweave Bandages, you have to depend on what seems to be a world drop.
The rules are still a little hazy, and the plans to get it seem to be somewhere between experiment and superstition: we know for sure that you need to have 390 First Aid already to get the book to drop (though you need 400 to actually use it), and we know that it can drop from almost anywhere in the world. But apparently there are a few places where it drops more often: in Zul'Drak, sometimes in Sholazar Basin, and sometimes in dungeons. Other than that, everything else is just rumors -- I haven't gotten the book yet, and I've been 400 since I had enough Frostweave to level up.
I heard it was on the AH for around 20g, but of course that varies by realm, and when I checked today, it wasn't on the AH at all. And we've also heard that once you learn it, it won't drop for you again, so there may eventually be an AH market for these -- until all potential sellers actually learn the recipe, that is. And then there's this, which just makes my head spin. We may see another level of Frostweave bandages in a future patch.
Very strange, and strange choice by Blizzard to do it this way in the first place. It also appears that a stack of Heavy Frostweave Bandages sells to vendors for only 5g, so the days of nabbing lower-than-3g stacks of cloth on the AH and selling them to vendors for a profit may be over. Which is fine, because your guild's tailor could probably use it anyway. But I am bummed I haven't see the manual drop yet -- the better my gear gets, the less the non-heavy bandages do for me.
Update: Yes of course they can't be on the AH, because as you can see in the screenshot above, the manual is BoP. Never mind. Thanks, commenters.