It might be wrong, but I have a source here that says the Lew Horton guns all have the K/L frame gripframe instead of the regular N-gripframe.

If that is true, then finding the correct combats shouldn't be that hard. I have seen them recently in the classifieds even. If you have any K/L frame grips, you may want to try them out and see for yourself. Obviously any of the square butt grips will fit over a RB frame, you'll just have the gap at the bottom where the frame curves in, but you can at least see if they fit right, where the top horns meet the DA hump.