Welcome to the Forum!
We have several grip makers as members here. Caryc, Pvt Schultz, 41magnum, and a few others I can't remember immediately. One of them should be able to help you.
I'm with flatgate on this one. I've heard that 41Magnum will make extended grips but I've not gotten it from the horses mouth if you will. I switched out the XR3-RED grip frame on my stainless Blackhawk in favor of the SBH variant. I make grips that'll fill the hand better, but you'll still have to find another place for that pinky finger unless you go the SBH or Bisley route.