I am working on building an old Raleigh Grand Prix and the rear derailleur was extremely rusty and didn't move freely. I disassembled everything, got all of the rust cleaned out, polished the cages, and greased everything with no issue. The problem came during reassembly. I over-torqued one of the allen bolts and broke the attached return spring. I couldn't get any pictures but.

Is there a resource for ordering replacement components for vintage parts or is it going to be easiest for me to just replace the whole derailleur?