I'm not sure if there is anything "boot grip" style (2 finger), rubber, and covered backstrap for s&w. But you could use a taurus 85 or similar stock rubber grip. It's all of tha above. Have to drill the bottom pin hole in a different location but that takes all of 10 seconds. Also maybe pop out the taurus emblems and stick some kind of plug in place of then. Ya know, as not to deface your j frame.
Can get them off of taurus website or find them on eBay etc.