UniKeep Game Cartridge Storage... https://www.amazon.com/dp/B07XZLZYYK?ref=ppx_pop_mob_ap_share

I think you'll need to just store them separately. GBA seems to be hard to come by for a good storage case.

Here's a binder that'll hold 10 GBA games on Amazon.

Ultimately the best bet is probably just to get a flashcart like a GBA Everdrive or EZ Omega.