Mag release spring?

If there's anyone in the area near you that sells music wire you can wind your own pretty easy. An Ace Hardware near me sells it. Five coils of .050"-.060" music wire should be in the ball park. I'm not taking one of mine apart to measure it, but it's bigger than the .040" wire I do have. Perhaps someone who has a loose spring could give an exact measurement. For a single torsion spring, make a plate with a rod sticking up for the wire to be wound against, and a short pin near the pin to hold the bottem end of the wire as you wind it. You can make a quick winding tool by drilling a hole in the end of a rod the same size as the pin, and filing down the end so that there's a little nub about as tall as the wire to turn it. Leave the ends long and press down slightly as you wind the spring to keep the coils tight. When you're done bake it at 500 degrees for an hour to stress releave it.
Here's a picture of a winding jig I made to make a double torsion spring for a suomi conversion I was working on. In this case since its a double torsion spring it uses a slot to hold the bottem of the spring, where as yours would use a short pin. You can just make out the hole on the bottem of the "T" handle tool with the small drive nub that turns the wire.