First, where are you? Assuming your in the states or Canada...You can order a replacement CGA320 from places like Kegerators, Wine Refrigerators, Water Coolers, Beer Taps, Compact Refrigerators | BeverageFactory.com
If you are looking for a machinist, first try the yellow pages under Metal Fabrication or Machine Shops. Call and explain what you need and ask for recommendations if they can't do the work. Calling a welding shop may also get you contact leads. Also, there is at least one machinist here at APC. His thread is maybe a month old now and it is an aquascaping journal about a 60 or 90cm ADA tank. He might be able to help or give other suggestions.