There is one on Ebay in Minnesota it's listed as a 235 but if you look at the picture it is a 261 . item number 183510014163
Other than that all the 50 series chevy farm trucks and larger had 261 engines. There is some info on this site that will tell you what to look for.
I am currently building one for a future project , not sure if i would part with it or not.
