If you're in the U.S. the short answer is, you can't.
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Depends on where you bought the gun. If from a store they should have the info. It might even be on your receipt. If you bought at pawn shop they usually include that info on the receipt. If you bought from individual and your state doesnt require registration you're out of luck.
Go the the gunshop or person you bought it from.
I just bought a 58b and found the magazine at numrich gun parts.
If you just bought it and ask the police to check it and then it turns out to be stolen, in all likelihood you'd be in no trouble at all; you're just trying to verify the gun is clean. If it does turn out to be stolen, however, the police have to confiscate the gun, so you'd be out whatever you paid for it unless you filed a civil suit against the seller.
Blue Book of Gun Values, gun shop, gun shows