Yep, two actually. R&D is run by Kenny Howell and ArmSport is run by R.L. Millington. Get ready for some sticker shock. Millington will only work on 2nd and 3rd generation Colt's and the conversions run about $1000 to $1300 with ejector. His lead time was 18months about a year ago when I emailed him. Far as I know, he is among the very best.
R&D, if the website prices are any indication, is much more affordable and they will do Italian replicas.
I'm hoping that the Italian replicas will catch up and start offering more Colt guns as cartridge conversions. We have the 1851 Navy and 1860 Army but I'd still like to see the little pocket guns as well as the big Walker and Dragoon models.
Both `smith's are well-reputed and have done custom guns for Tom Selleck. Both personal and movie guns. If you're interested in these guns I highly recommend Dennis Adler's book on the subject, "Metallic Cartridge Conversions".