Scour junkyards. Post a WANTED add on craigslist, or facebook. That's how I found my first Buick 350. Don't be afraid to travel to get one either, as a last resort. I went to Omaha from Des Moines for my current 350. Any 70-76 pontiac will 99% of the time have a pontiac engine in it. Rear distributor, cocked at an angle is the tell tale sign. Chevy and olds have the distributor in the back as well, Olds has an oil fill tube up front coming out of the block, chevrolet doesnt. Chevrolet has the dumb distrubutor through the intake design, pontiac and olds do not.