You are looking for a production jeweler also known as a manufacturing jewelry company.
Here are some Options:
1) Check out http://www.racecarjewelry.com . They do complete production services in gold, silver, etc and advertise frequently on the Ganoksin (Thai for Art of Gold) Digest. No affiliation. Just seen them on the list for years and remembered their name.
2) Go on any of the jewelry/gemology forums and ask for recommendations: http://www.ganoksin.com/index.htm; http://www.gemologyonline.com;
3) Do a google search for "production jeweler" or manufacturing jeweler and you can probably find one that is local to you.
4) Ask your local "custom" jeweler for a recommendation.
5) Most larger cities have a section where jewelers congregate. In San Diego it's the Jewelry Exchange building on 5th street.
6) Check the trade magazines: Lapidary Journal, Jewelry Arts, Metalsmith magazine.
Hope that helps and good luck.