Red"]Here[/COLOR] is Wolff gun spring's contact page. I e-mailed them and asked about my Rossi snubbie. They posted back and said to use the S&W J-frame kit. The only springs they list are for the Bulldog model. Can't hurt to ask, though.
At one time there was a Trapper Spring Kit made for Charters which I believe had 3 mainsprings. The firm operated out of Michigan and was run by Lynn Alexiou but forget the name, may have been Bullseye Gunsmithing. Natchez Shooters Supply sells the kits but they have no Charter ones currently.