The engines are out there but it's not the kind of thing that will be easy. I looked for quite a while before I found an older rebuilt on Kijiji for $450.
Try a wanted ad on Kijiji in the farm implements section. Still lots of these engines on the back 40 and not really front and center in the farmers mind.
There is a wreckers in Elfros, Sask,(Elfros Auto Wreckers) and one in Webb, Sask (Jensens) with lots of older vehicles.
For me, the hunt for parts is half the fun of an old car/truck
I have the bare block for rebuilding (25 inch 251) and my nephew has a block as well, 25 inch but unknown CID. Mine is a freebie and his might be $100...both in Calgary.