I have found a great source for the 64 C10 interior paint. Mark at A1 Auto Parts in Buckeye Lake, Ohio can fix you up. He took a Paint Matching Paint Scanner and scanned the interior of a customer's 1964 C10 with 30k original miles on it. He mixed some up for me in spray cans and it is a perfect match. He uses a good quality spray can, and the paint comes out fantastic. Great guy to deal with. He can be reached at (740)-928-0333 M-F 8am-6pm, Sat 8am-4pm Closed on Sun. Times are Eastern. Just ask for Mark and tell him Calvin from Oregon sent you.
