I've seen some shops that set up a non refrigerated soda display like what you'd see at the gas station to display their stock. Another idea I've seen is large empty coolers with soda's just dumped into a giant pile where people dig through them.

There's 3D printed stands that are made as well for actual collection displaying from a few small companies, though I don't think that would really work for you guys unless you just wanna show off your more pricey ones in a display case.

Also, I'm not surprised they sell well, they're really fun to open. And, some of them are super good looking even in comparison to pops. I'd like to get a batch of random soda's to crack open for a chase hunt for some video content, it's very similar to opening up Pokemon cards in a way, which just makes it fun to do and watch.