My kit from Tapco was missing the spring for the lock on the folder mechanism.
At my local hardware store "Smalls Pro Hardware" they have a huge selection of springs.
I bought a No.3 and No.6 spring. The No.6 is the same diameter, but longer.
The No.3 worked just right for the folder. It fit around the bolt/button and was the right length. It could be slightly shorter maybe, but worked great.