More specifically, the AC DELCO radiator on rockauto.com - it's going to cost you quite a bit, though. Be sure to utilize the Blazer Forum's 5% discount code!

New part number for that radiator is 20837.

 

Remove the cap and check the inside for cracks. Sprinkle some baby powder inside and shake gently to distribute the powder, if there is a crack you will see it plainly. Even a slight crack can make the Blazer run rough or even backfire. I have found new parts with cracks or other defects. Good luck!