If you are looking for vinyl for the sides of a cab and want to avoid seams from shorter rolls,
The Playdium Store (formerly Starburst Coin) at 401 and Martin Grove is a Happ distributor and stocks
their stick-and-peel vinyl. Just quote the Happ part number (applies for most common stuff in the Happ catalog as well).
I've used the 40" Black Pica on four cabs for both refinishing the sides and as control panel overlays. It's easy to apply, durable and looks great -- I'll be heading over later this week to pick up some more (if I was smart I would have gone on Saturday when everything was 25% off!).
It is more expensive than the 24" rolls (although last time I bought some it was significantly cheaper than what Happ charges direct), but I like not having any seams.