Those guns are rebranded CYMA.
I'm guessing from what you said that the piece of metal that broke is the small part on the lower receiver, forward of the charging handle.
The only place you might find a new receiver is getting AV'd and maybe you can find one in the classifieds or a retailer might be able to get one for you. It's the same CYMA receiver as on the AKS-74U and AKS-74. But honestly, considering how much a new AK-105 will cost you and how much you'll pay just to get a receiver custom ordered, you're better off just buying a new one.
Otherwise you'd have to get an AK74 receiver, which will still cost you almost half of what the gun costs even for the crappiest one (Element), and you'll be limited to a full stock.
Your best bet is probably to try and repair the current body. Use an epoxy to reattach the broken piece. If you don't know how to work with epoxy, take the time to read and learn first. If done properly it'll be hard to tell it was repaired. And then stop letting the bolt fly like it's a real gun, there's no reason for you to be doing that on an airsoft.
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