Go to the "bad side of the tracks" and walk in. All towns have a bunch of generic machine shops that can manufacture. Look for welders, machinists, sheet metal and that type of thing in the name. Then walk into the office.

Note that few of them will do the design/engineering work for you. But if you have a "blueprint" they will build it. Be prepared to pay - they are all making good wages for your city not third world step above slave wages.