The spring is a flat leaf type spring. A photo is available on the Numrich site. Go to manufacturers and select 'S' for the S&W listing, then to .44 Double Action for the part listing photo. The spring can be cut from a clock spring. Good luck.
I think you're gonna just have to make one. Like Mike recommended from a watch spring or so many other comparable springs. It's a smaller straight spring but getting the thickness and length correct can be a challenge. Also putting it back in place under tension is tricky.
Hopefully the little retaining pin will come out. It's pretty hard to snap one of these when they are in place. Did you forget to bend it up before you removed the pawl/hand? Or was it cracked? Sometimes that little pocket or the hand flat is full of crud and overextends the little spring.