You're a new member and this is a very odd request. Maybe the guy that sold you the hood isn't responding because giving you the VIN # off of his car was not part of the deal related to selling you a hood. So, why would somebody from this website "throw you a VIN" from their own car - the VIN is, of course, a unique identity plate that ties that specific vehicle to that specific owner, assuming it's a registered driveable car?
Why can't you use the VIN from the GTI you're rebuilding -- that's really the question? If the car was in a serious wreck, then it would have a R-Title for a salvaged vehicle -- but, it would still have its own VIN. Also, why do you say, "rebuilding your car," but you never say what year you're rebuilding, or even that the vehicle is even a VW GTI. So, again, why are you asking people from this website to "throw you a VIN" and what "sheet" are you trying to put someone else's VIN on? Clearly, whatever you're doing isn't legal, if you need some random person's VIN to do it, and the fact your account is so new and the way your story reads -- "hey, I bought a hood off of Facebook"... what does that have to do with anything and why would a guy selling you a used hood give you the VIN off his car in the first place?