You guys may already know this - if so my apologies for bringing nothing new to the table. I was having problems finding parking brake link springs for my '56. The usual sources do not carry them - MAC's, Carpenters, etc. Turns out they are the same as the '56 T-Bird, same part number. TA601-2. National Parts Depot had them in their 55'-57' T-Bird catalog. $1.25 each.
The other option is in the "sticky" file when you do the self adjusting brake upgrade the springs are in the kits.