If it is a criminal case, it costs you nothing. The cost of a subpoena to the state is insignificant. But it sounds more like you are really talking about a search warrant. If there are sufficient legal grounds to issue one is another issue, but it does not take much these days. It is a standard investigative tool. Cops look at pawn shop records all the time without subpoenas or warrants.
The police usually just could get a search warrant for information on that particular item. It would not be until a criminal trial that they would issue a subpoena to the store person who would provide a evidentiary foundation for the entry of the records into evidence
Do some research on your state law. See if a place buying stolen property can actually require a subpoena/warrant from law enforcement in the first place. A store buying second hand merchandise from individuals might be regulated like pawn shops.
The other approach would be to sue the person civilly, name GameStop and issue a subpoena to them. If you name them a defendant, then you can do discovery against them too. I would argue they are knowing dealers in stolen property, subject to civil RICCO. That would get their attention. This would all be expensive if you needed an attorney to do it.
In the case of Microsoft, yes they would need to be issued a subpoena which could be criminal or civil.

