I have a DIY black pipe air line fir a compressor connected to a blaster and paint gun.  Now, I need a bit more skill to do some re-piping and water collectors.  The DIY is going to involve cutting pipe and adding sections.   Starting g to get a little ahead of my skills.

Is this something a local plumber is familiar with ?

Black pipe is used for gas lines, some plumbers (but not all) also are pipe fitters and that's what you really need.

Sounds easy to find ??

There should be a threaded section that can be unscrewed and another length of pipe used for the length needed.

Home Depot will cut and thread pipe for you. Just pick out a longer pipe that's in stock and they do this service for free.

Mount a water vapor trap at the end of the pipe and use a quick connect for your flexible hose. It should be an easy project, but not sure if your going through walls or what else is involved with your particular project....

Most all professional companies that use compressed air (outside of medical) use black pipe.  1/2" should do.  

Depending on your use you may want to incorporate a dehumidifier into your lines.  Over time the moisture can cause rust which can flake off and jack up your tools/machines/end product.

Handyman / residential plumbers probably won't be familiar enough to address your concerns but commercial / industrial plumbing companies should have no issue with that sort of project.