I didn't think there were springs at the interior handle? The latch itself has a spring which returns the handle though the flat linkage.

If you're talking about the springs that keep the EXterior handles from drooping, Jim Carter was where I found mine. Maybe they have the ones you're looking for as well?

'69 1/2T stepside, Sea Foam Green, 250 L6 w/ 3 on the tree, not an option on it, in the family since new.