1966 Plymouth Valiant 200

Welcome from Gig Harbor! There's an excellent source of reproduction parts in Lakewood, WA called Layson's. I really doubt that Legendary makes seat covers for 4 doors. If originality is a priority, SMS Auto Fabrics near Portland will have the raw materials that a local auto upholstery shop can use to make your seat like new. Also, have your original (if it is) radiator fixed at a local radiator shop.