I would have posted this in the Class A and I'll ask that it be moved. It's not encouraging that they cannot find what sounds like a simple part/connector.
I looked at the Yahoo Monacoers parts list for you and could not find a break down, just various manufactures of the instruments.
Sounds like it's a simple push to seat connector. I would cut 1/2" off of the plastic air line and see if it will hold. The connector should be screwed on the gauge so if the above does not work, I'd replace it. A large NAPA store should have them.
