You really ought to try doing it yourself. In the long run it'll save you money, increase your enjoyment and pride knowing you can do it yourself, and you can paint more than just engines.
I have a very old compressor (Miller) and a not so old airbrush (Badger Crescendo 175). If I had to get another it would be an Iwata brand:
http://www.tcpglobal.com/airbrushdepot/iwata.aspx
If you still want to get someone else to do it, do what Tex (Steve) said and do a search on the forum, there's a few well-known painters who can do what you want.
Here's a Williams E7 I stripped and repainted for Seaboard Air Line:
A modified MTH CA-1 caboose:
A Weaver PS2 2-Bay Covered Hopper:
A MTH 0-6-0:
I'm by no means a great painter, but if you take your time you can turn out a few nice pieces at a fraction of the cost.
If you do decide to ever get a compressor and airbrush, get a compressor that is quiet. Mine makes a racket and I find the noise alone makes me get in a rush. I had the Iwata girl at the IPMS show in Va. Beach a few years back give me a demonstration and I couldn't even hear their compressor, which was less than 5 feet away.
