Have you looked at a Hemmings book? Before the internet it was known as the car collectors bible. If you're looking for NOS obsolete parts, here is where you'll most likely find it. Here are a few ads I pulled off their site, but nothing beats the printed book. The site is
www.hemmings.com, I just did a general search. But this will give you an idea of the things you can find.
There's also eBay. But you'll have to be patient if you're waiting for something in particular to show up. It's always better to actively pursure things you need.
The hemmings ads:
DOOR panels, dash pads, steering wheels, columns, obsolete parts, 1950-2000. CADILLACs Only, 818-772-0707
CADILLAC, large inventory parts 1950s to 1980s, solid California sheetmetal including doors, fenders, decklids, skirts, grilles, die cast trim, moldings, interior trim, body fillers, bumpers (original or replated), a/c, hubcaps, gas tanks, radiators, 30 years' experience. Bob's Cads, 408-984-8877, CA.
1971-1985 ELDORADO NOS, repro items: 71-85 hood ornaments; hood ornament base; 75-76 rear quarter panel script; 74-85 hubcap medallions; 74-79 hubcap wreaths; 72-85 trunk scripts; 76-85 trunk wreath; 74-85 front bumper impact strips; 73-78 filler beneath fuel door; 74-85 fender and quarter panel extensions; 71-85 driver's side remote mirrors; windshield washer bottle; radiator overflow bottles; 73-85 front end fillers; 73-76 bumper reflectors; 74-78 rear chrome bead molding; 75-85 hood hinges; thousands of other parts available in our free catalog; MC, Visa or COD. USA Parts Supply, 703-335-1935, VA.