I just used car-part.com and I found some here in Idaho. The yard in Lewiston has one for a non-AC car for $65.00. They do ship parts, I got my bellhousing for my 73 wagon from them. Their number is 1-208-743-9505.
Buying one used, I would have it pressure tested and checked for leaks at a reputable radiator shop (I have mine done for $15), and if need be have it sealed up if need be (my shop does mine for $25-$50 depending on the repair).
The great thing about the original radiators is they are brass and will last forever compared to the plastic modern ones.