GIFs aren't meant to be kept hidden in a folder, tucked in a dark corner of your phone or computer -- they're meant to be shared. Google is making it much easier to do that on mobile by putting shareable GIFs in their own section under Images. Just do a search for the reaction GIF you have in mind and hit the Share button under the one you've chosen to punt it straight to Gmail or to a convo in Hangouts, Android Messages and WhatsApp. The sections shows options based on how popular they are, so you'll probably find some good candidates without scrolling down too much.
If the selection ever looks lacking, it's probably because Google gets its shareable GIFs from content partners. All the options in the section come from the company's partner streaming services, movie studios, YouTube and other willing participants. You'll likely have a lot to choose from as the feature becomes more available, though, since any GIF creator, platform and content provider can contribute.
Shareable GIFs are now available on the Google app for iOS and Android, as well as on Chrome for Android. The company is also working to bring the section to all mobile browsers, so nobody has to dig into their GIF folders anymore.