John.
I purchased our new steel/copper radiator from Radiator Supply House, 4432 Hwy 20, Sweet Home OR 97386. Phone # 877-615-3002. IMHO they build a quality product that was an exact fit. They will need the number ID from your old radiator, you should find that number on the sheet that has all the information on your TV's, Microwave, Air Conditioners etc. Our information sheet is located on the back side of a cabinet door above the bathroom sink.
In 2016, the radiator alone was $3750, you should expect shipping charges in addition. As suggested, this would be a good time to consider other changes like T-stats, ELC coolant, hoses and the like. If you have questions, feel free to contact me. good luck!!