If you know what radiator fits your Cobra then there are several places you can buy from, Jegs, Summit, O'Reilley's etc.
If you need a custom radiator you can have Brice to make one for you. They are a factory and make radiators for everyone. They sold me a '74 Mustang radiator that fit a Cobra I want working on. Cheap!
They have made custom radiators for me to fit various cars through the years. Brice has sold me aluminum tubing for air conditioning lines in my GT 40. I needed '7 pieces of two sizes.
Good people to do business with.
C,G, & J Inc.