Don't know of a site.. however autozone has a good radiator book (think its spectra premium) that has an illustrated section. I would tend to think that any good parts store should have a radiator book with an illustrated section though.
bttt, looking for same thing. trying to find a radiator that is about 16" to 16.5 wide and around 21 tall.. would be nice to be able to find an online radiator catalog with dimensions
Check with Performance Radiator, they used to have a book with radiator sizes. https://www.performanceradiator.com/ I put a Ford crossflow in my daughters 36 Chev PU, turned the radiator up on the end and changed the fill location.
I have found many good sizes from people on Ebay that sells them . They always list their sizes . Also try Griffin Radiator site . Have you tried a Goggle search ? Retro Jim
http://www.yourautocoolingsource.com Has a good selection of them and they list sizes and at a good price. I used a Dodge 360 radiator for my Chevy 350. Was less than 150 shipping and all
The autozone route can be kind of painful, for my 52 i went page-by-page through 40+ pages on their website. clicking each one that looked like it might fit ( inlet/oulet location and lenght vs width) I finally found one that was close enough, #433957, or cu957, bought it and made mounts for it. spectre's web site says its for a 1980's dodge cb300 w/ a 5.9L. So just be prepared to spend some quality computer time scrolling thru pages.