Check out classicairsoft.org
I'd recommend getting an LRB and keeping it as a classic instead of destroying another piece of history and making it an AEG
edit: if my memory is failing me and TOP used the same internals as STAR, then you have that weird gearbox that is hard to find replacement parts for, but if my memory isn't failing, then I think you can use either a V2 or V3 gearbox in it after some modification