Looking for Source of NSPT Plugs for A.I.R. Exhaust Manifolds

[Mike T.]

There was a recent thread that discussed the pipe threads found in Air Injection Reactor Exhaust Manifolds and mentioned that the thread is National Straight Pipe Thread (NSPT). When using the Dorman brand replacement manifolds and not intending to use the AIR piping system, there were two sources for plugs to seal off the AIR holes, Grainger and McMaster-Carr. I did find the NSPT tap but no listings for the plugs, whether hex or square hole style. Any recommendations for another source?
Thanks, Mike T Prescott AZ