My truck is a 1955 F250. I reused all my springs so I didn't have to go looking for any. I purchase a lot of stuff for my truck from midfifty. They have the retracting spring, it says for 48-63 trucks.
1948-63 Ford F-100 Brake Shoe Retracting Spring - 2035
They also have the Anchor spring, which I think is the one you are looking for?
1948-63 Ford F-100 Brake Shoe Anchor Spring, Above Adjusting Screw - B5A-2049
I assume you have a 66 though? So they may be slightly different. I wonder of O'Reilly or Napa might have them. Some of this stuff was so standard that they often have some parts we need.
If you need anything else, just let me know. Sorry for the delay. I saw the message, but then forgot how to get back to it later.