Until you find one, you may want to try and make one using an altered spring from an AR15 build kit. AR's use several different types of small springs that you can easily cut to size. I used one for the sight slider on my M1916 and it worked really well. You can use the spring on the other arm as a guide for size. You can buy full replacement spring kits with all of the different sized springs for ARs for $10-15 on line. Hope that helps!