many parts for the classic Penn reels are available on Ebay. You could pick up a "beater" reel to use for parts. Also, you can try your local flea market. I picked up a sweet Penn 712 greenie earlier this year for around 30.00 at the Taunton Flea . It works great. Here is a link with some Penn history in it: http://www.tattoostackle.com/americanclassic704.php
Try Bucko's , they've always been great for parts, even with really old stuff. Penn used to supply parts also, don't know if they still do but it might be worth a call.