I bought a pair if side pull calipers for a mixte bike I am working on. When I got them I found that the finish on the wishbone-shaped spring had worn off where it met the slotted posts coming up from the brake arms, and the parts wanted to stick together. It took some extra force to break the arms free from the worn spots on the spring, and the spring on one side of this caliper actually stayed stuck to the post, all the movement was on the other arm. Rather than try to find new springs, I came up with the fix shown here. This is PTFE tubing cut into pieces and slipped over the spring wire. Now the edges of the slots on the posts dig into the PTFE and hold the tube while the spring moves nicely inside the tube when I squeeze the brake arms together.
The spring wire measured about .098-.099 inches, which is about 2.5mm, so I bought a 1 meter long piece of 3mm ID 5mm OD tubing on ebay, it seems to be a pretty common size.We'll see how it works, see if the tubes walk off the end of the spring, but just operating them by hand it looks like they will stay put