A spring needs to be heat treated and tempered to a relatively low hardness to make spring steel (spring temper). If you lack the equipment to do this Texas Knifemaker's Supply has 302 stainless steel for springs in 3 sizes ($1.35 for a 1 foot section) on page 44 of their catalog. I do not know if it is on their web site. They carry pinstock, but if I remember right I bought mine from Jantz, I think the selection and prices were better.
Part #'s and sizes of Spring Steel from Texas Knife:
SM001 .088 wide x .062 thick x 12 inches long
SM002 .120 wide x .062 thick x 12 inches long
SM003 .170 wide x .062 thick x 12 inches long
Shop around for prices, I think Texas knife had better prices on sheet stock and some bar stock while Jantz was better pin stock prices as well as some other items I ordered lately.
I also enjoy working with Alpha Knife Supply
http://www.alphaknifesupply.com They are always very pleasant to work with.