An IBM M1 carbine would be an excellent find.
I recommend mailing in an order to CMP for either a rack grade carbine for $495 or for a service grade for $575. It'd be a 3-6 month wait, but you'll get the piece of history you want.
CMP M1 Carbine Sales
Personally I'd order the service grade. Only problem is I don't believe carbines ship with magazines and if you plan on shooting it, ammo is expensive (more than most) and hard to find.