I will suggest looking on Gunbroker website. Search words "gunbusters". This will bring up several gunbusters companies, which sell parts kits. (gunbusters 63005 [st louis] , gunbusters 53327?, gunbusters ne [new england], gunbusters se [southeast])These are disassembled guns required by law for whatever reason to be legally destroyed. So they disassemble the gun and crush the receiver. Everything else usually is sold to the buyer: the stock, hand grip, handguard, trigger assemblies, and barrel, although sometimes everything is not included... Little springs, pins, etc can get lost. You have to see the photos & make a determination if you can rebuild the gun.
Gulfcoast gb (gulfcoast gunbusters) must be searched specifically by seller's name.
Their weekly auctions start on Sunday night and end on Sunday night. I have bought many, many parts kits from them and never had a problem. Rifles, pistols, shotguns, etc. all disassembled parts kits.
Every now & again they offer a real gem that goes for cheap. But most people know what they are looking at.
Watch it and wait. I'm certain the item you want will come up sooner or later... It's hard to snipe the auctions, however, because when it gets down to ending time, every new bid puts 15 more minutes on the clock.
Good luck.