That's the problem. Who?
Yes, others do color case hardening, sometimes quite well. Turnbull, though, is pretty much acknowledged as the only place to get *the* color case hardening you want. For example, if you want period-correct color case hardening for the restoration of an old gun, Turnbull is the only place I know of that can be reasonably sure of turning out a finish that actually looks like it would have come from the original factory at the time of original manufacture.
Start a thread on how you decide who to use. If there are other folks out there doing color case hardening as competently as Turnbull, I really want to know about them.
This project has fallen down the list, still in the top 10, but not near the top. May take a while. Heck may end up with them doing just the two halves with me doing the rest.