Garth's Aerosmith Shirt
The Aerosmith Aero Force One t-shirt that Garth wore in Wayne’s World might be the most infamous shirts that Dana Carvey wore in the film. To give you some background, this shirt references Aerosmith’s fan club, Aero Force One. The fan club gives it’s members official Aerosmith t-shirts and that is where this shirt originates from.
The shirt is most likely from the late 80s and is probably no longer produced; I couldn’t find anywhere that sells it, but there was some ‘evidence’ that they might still print some of these every so often.
The good news is that if you’d like to print one of these shirts yourself, it looks like a few days ago a DeviantArt artist has re-created the graphic on the t-shirt and might give it away, if you ask nicely. I’d suggest trying ebay or etsy if you really want this t-shirt.