Well since it's probably not registered, and you probably cannot find the previouse owner to sighn the greencard, the state considers it evil and it must be melted down no exceptions it doesn't matter how rare or valuable it might be, or what the circumstances are, you must be a good sheep and turn it in for destruction....
Thats what the law says on the other hand....
WARNING: THE FOLLOWING STATEMENTS ARE PROBABLY HIGHLY ILLEGAL IF YOU DO THEM, IF YOUR CAUGHT YOU WILL BE ARRESTED AND WILL GO TO PRISON, AND, OR BE FINED SO DON'T DO IT, THIS INFORMATION IS FOR PURELY INFORMATIONAL/ENTERTAINMENT PURPOSES ONLY DO NOT DO IT, INFACT DON'T EVEN READ IT, AND I OFCOURSE HAVE NEVER AND WOULD NEVER DO THIS BECAUSE IT WOULD BE WRONG, AND BY THE WAY I AM NOT A LAWER, AND YOU SHOULD TAKE NOTHING I SAY AS LEGAL ADVICE, OR SERIOUSLY IN ANYWAY, INFACT YOU SHOULD JUST IGNORE IT!!!!!!!!!!!!!!
....you could call an out of state police department in a state that doesn't require registration, and make up a story of why you want them to check the serial number to see if it's stolen, tell them your interested in buying it or something (CALL FROM A PAY PHONE, NOT your homephone....) as was suggested above, if it comes back clean great, if not do the right thing and tell them where they can find it, but you might have some 'spainin to do.... If it's registered to someone get in touch with them find out if they want it back, if they do give it to them, if they don't see if they will sighn the greencard, if they will great, then do the transfer the right way, if they won't then your probably shit out of luck, and the pistol will probably have to go to the smelter.... If it's not stolen, or registered then you can do one of two things:
1: Give it to a friend or relative in a non registration state, then have them give it back all going through transfer dealers both ways, (if you need to find a "friend" ask around the board I'm sure theres someone who would be willing to assist, if not for free, then maybe for a small fee, just cover there transfer, and shipping costs....) then just get a purchase permit, and have it registered like you would any pistol, and your done the pistol is now 100% legal....
2: Go get a purchase permit, say that you're buying it from out of state, or some other BS story, then go through a transfer dealer (or maybe go through the transfer dealer first if you want....) just mail the pistol to the transfer dealer as if it's comeing from out of state eighther don't use a return address, make one up in a non registration state, or use a real address from a friend or relative thats in on the scheme from a non registration state, preferably mail it from the state you say the pistol is from, and preferably near where the address would be, or is in that state, atleast in the same city in that state where the address is supposed to be or is, I could be wrong but I think all the dealer needs is the name of the sender, so make one up, or give him the real name of a friend, or relative who lives in the non registration state that you say the pistol came from, as far as I know federal law says nothing about telling the FFL a fake name when transfering a gun TO the FFL, I.E. the sender, and there is no requirment for the FFL to get the senders ID, or attempt to verify it in any way, so as long as the FFL isn't in on it there breaking no laws eighther, obviously use your REAL name when filling out the 4473 just like you would any gun, once it's transfered to you from the FFL just treat it as you would any pistol fill out the greencard, and have it registered, and your done, the pistol is now 100% legal....
There are no federal laws broken that I'm aware of with eighther method particularly number 1, number 1 only "bends" Michigan law, technicly the state police website only talks about transfering the pistol to yourself, so you can just play stupid, I haven't actually read the law so this may not even violate the letter of the law, so it would break no Michigan law eighther.... As for number 2 it's more questionable as far as Federal law, but I still don't think it violates it, Michigan law however is most likely certainly "bent", if not broken entirely, I'de go with number 1 if I were you....
AGAIN THESE SUGGESTIONS ARE FOR INFORMATIONAL/ENTERTAINMENT PURPOSES ONLY DO NOT DO THEM