This page lists a lot of them:
http://www.erareplicas.com/427/427options.pdf but mostly, you need to go visit them. If you've seen anything, anywhere, that you like, bring a picture of it along with you. What I did was just tell them what I wanted, showed them pictures of stuff that had been made for a CSX owner that I wanted, and then specifically
did not tell them how to do the fabbing or how to build it. I then just got out of their way.
