I never heard of any kit to convert any of those revolvers to .22 caliber RF; it would have been a one-off gunsmith job. At one time, Numrich sold leftover* Colt barrels and cylinders in .38 Special and .357 Magnum for the SAA and many of those guns in calibers for which ammunition was no longer made or was scarce were converted. I have no idea how many rare calibers might have been converted at that time, but I suppose a good number were.
That was when Colt had discontinued the SAA and sold off not just parts but the tooling as well. We all know how that turned out.