Places to find a QJ: the best would be a swap meet. I find them anywhere from 15 to 30 dollars. (although its not the best time of year for swap meets. Usually those start in the spring). Internet could also be a source, like this site hear or even craigs list. Next in line would be the junk-yard (politically correct term would be automotive recycling yard). AND, you can find QJ's in other vehicle's other than GM one's. (like mopars in the mid eighties also used QJ's).
Where are you located? maybe someone on here would be nearby that could sell you one. I think am early 70's chevy type would work ok on the 6 cylinder.