Internet resources can be difficult to find, as most search engines (notoriously Google) will bring up quite a few blind links and irrelevant results. Here’s a list of sources that I have used and recommend:
Parts Sources
Thunderbird Headquarters has a PDF version of their catalog available, though it can be difficult to find the exact part you need in that format. My local mechanic buys parts from this source with good success.
Bird Nest allows you to search and shop on-line; they also have a nice selection of used and rebuilt parts. I’ve bought many items here and have been happy with both the quality and service.
Dennis Carpenter also has decent prices and a good selection, but they are across the continent from me, which usually translates into slow shipping speeds.
I plan to replace my steering box soon, and when I do, it’ll be swapped out for one from Red-Head Steering Gears.
I don’t often go looking for NOS parts, but did when I had an old 62 F-100 pickup. A hard to find part can sometimes be had from NOS Parts Limited, Rear Counter, or Henry’s Parts Depot.
I only have second-hand information on these parts sources, so your mileage may vary here: Thunder Cars and Parts, Thunderbird Ranch, Bob’s Bird House and Pat Wilson’s.
Forums and Clubs
Discussions about Thunderbirds can be found by navigating through the Thunderbird Forum, the forum at Vintage Thunderbird Club International, Love Fords or the Ford Muscle Forum.
Paint
Trying to match a paint color? PaintRef.com appears to have the tools you need.
A forum writer noted that interior paint can be purchased in spray cans to match the original from Automotive Touch-Up.
Miscellaneous
Shop manuals can be found at books4cars.com.
You can’t read forum posts too long before finding yourself sent to Jim Wulf’s site.
Wiring diagrams (both page 1 and page 2) are on-line at the old car manual project site, though it can be a little difficult to follow a circuit from one page to the next.
Specifications and and a variety of vacuum diagrams for the Flair Birds are also available at the Thunderbird Ranch site.
My own 64 (VIN 4Y83Z176987) is listed in the official Thunderbird Registry.