Paul:
kind of ambiguous question.
what is the application here ? If you are talking about a stationary engine that you run on a bench or table or at a show. Any basic air regulator should work . I suggest using an air filter and a gauge as well.
1/4 npt seems to be the norm for airline fittings at most shows.
Also when you get a chance please post an introduction .Tell us a bit about yourself your shop and your interest in model engines.
Tin