It's a mouse trap type spring where the latch pivot pin runs through the loop in the spring. Get a spring with a long straight section and has about 1/16" wire size. Clamp a bolt the same size as the pivot pin (or one size smaller)in a vise and using two vise grips wrap the spring wire twice around the bolt keeping the loop as tight as possible. The original spring had two legs to the latch but since this will only have one you can file a small notch in the release lever and latch housing for each end of the spring wire to fit into to keep aligned. You will have to experiment a little to get the two legs at the correct angle and proper tension when the pivot pin is through the loop but it's not rocket science.

Evan