What kind of welder (person) do I need?

Since I don't have the welding skills I need to make my next project happen I've come here to figure out how to find a welder with the skills I'm looking for. I've got a project coming up where I need to source and modify a pressure vessel about the shape of a LP holding tank, 8-10 ft long and 40-50 in diameter. I need to take one rounded end off and replace it with a flat steel plate. It needs to have various openings added to include ports for pressure gauges as well as inlet and outlet valves. The vessel needs to hold 45 lbs working pressure and withstand a structural integrity test of about twice that.

Although I don't personally know any welders who can do this kind of work, thankfully I have enough connections I could probably locate one with a little direction. Since getting this made could end up costing $$ I'd like to find someone who does this kind of welding professionally but is open to a side job. My best guess is that boilermakers or pipe fitters would be the kind of welder who could help me out.

Could anyone suggest how I can find a welder with these kinds of fabrication skills?