Yes, I realize it is a one way valve. We have them at work. I couldn't recall if the air flowed or not when the valve was opened.
If you don't get any satisfaction through Scott, you might try "Dalmation Fire" for thread information and possibly a fitting. There is a system available that will bypass the one way valve but, it has a hefty price tag (~$300 IIRC). You're chasing the least expensive route with what you're trying to do but, I'm not sure if what you're looking for will be available. You may have to get "an adaptor, to an adaptor, to an adaptor" type of set up. Another option might be to simply replace the valve assembly. If you end up looking into that route, send me a PM. I have an older valve, that will be a direct swap, that I can send to you. Those valves should be screwed in to a specific torque but, I don't think they use any loc-tite on the threads, since it is designed for breathing air. Point being, you may have to take it to a shop to get the valves swapped and a fresh (sacrificial) o-ring installed.
Best of luck with your search!!
Tom