I know very little about quail… But I would guess that anything that would work for chickens would probably be good enrichment for game birds in general; things to climb, maybe tunnels to run through/explore, novelty items are always good (like a ball or crinkled up paper, or anything new and different from what they have now), different kinds of food to mix things up, and different ways of feeding them (feeding from a bowl vs scattering the food in bedding vs stringing it up somewhere/mounting a feeder etc.) I don’t think game birds tend to really be interested in toys and such, but if nothing else, toys would make good novelty items for them to investigate. Different textures would be good too; a natural tree branch with bark vs a plastic crate, etc. It might also be fun to grow them a little patch of grass or some other safe plant in a tub that you could put in with them, so they’d be able to explore the plant and check out the soil. Different substrates would also be good.
Anyone else with ideas is more than welcome to pitch in!
I’ve been researching these guys.
Above all, give them a dust bath! They’ll love it. A big pile of straw and a heap of dirt to play in is also good. Most of the above suggestions should also work, but especially new foods. Live insects (not collected from outside in case of diseases) would be great toys/treats.