It feeds like a subgun. Double stack, Double feed. That narrows your sacrificial choices. Plus I know of a few attempts. They never work right. Someone is selling some now I think.I don't see anything about the mag in the pic that dissuades me from modding another mag to fit...
Granted if you are looking for a "GB" mag for GB, and only such, then I understand.
But a mag that will fit and function well for a shooter, I think I can do it.
I do not have a GB to try...
Joe