So much depends on what exactly you are looking to do… but you will have no problem finding contacts. Perhaps if you describe precisely what skills you require, I can suggest some folks? LA is a fabulous place to be, there are many options.
“manufacturing houses” fall into numerous categories. Some are vertically integrated (print/mill, cast, finish, set, etc etc). Some just cast. Some just set, some just finish, etc etc.
If you are looking for one-off FABRICATION, and you want the finest quality, I personally think the world gets small quite quickly There are perhaps a dozen or so people here in the United States I would call to fabricate me something out of platinum, for example. @JimGrahlDesign is a friend of mine, and he is just outside of LA. Just an example, as selection of service provider depends SO MUCH on what you need done. Most Orchidians will tell you straight up what they do and what they don’t do, and who does it well.