Wrecking yards, or depending where you're located another member here might have a spare (I have several in WA). If you're not trying to stay 100% stock, it was an easy swap for me to put a '70's/'80's Dodge truck tank inside the frame under the bed (PM me if interested in details). Others prefer a van, Ramcharger, or car tank in place of the spare tire. So you have several options.