I found this guy who can do good water transfer decals
Have you tried any of his products? It looks to me like for large outdoor stuff - very thick and heavy
I found this outift:
http://www.echomtn.com/custom.htm
They will do brass photoetching too.
Why would you be interested in having someone put decals on your trains? Unless you have tried it and found it beyond your capabilities I wouldn’t even consider it. If you have tried it, forgive me.
He does water transfer water decals for models too. He also does custom graphics for cars. I will put a picture up soon!