I'm sure they carry 1/2 hardware cloth. If you're handy with building I'm sure that you can build a nice cage. There is a cage section on TSB. You can get some ideas from cages others have built.
One thing I would encourage you to consider before getting in too deep ... Flyers are nocturnal and that is when they want to play. They are also colony dwellers and are quite social little critters. They require a commitment of time. I haven't gotten a full night of sleep since I got my little guys ... BUT I sure do love them. I feel like they need my attention everyday. I can't just leave them in the cage. They need interaction with their people to be healthy mentally. Some develop neurotic tendencies ... like repetitive flipping. That is why I feel they need interaction every day.
With that said, they are amazing little creatures. When you see them fly for the first time, it is MAGICAL. It is worth every minute of sleep that I have given up for them.