I assume you are talking about the connector for using city water? Looks like this:
Camp-Inn sells them so you could call them and see if they can 2-day one to you if you need it right away. Mine is in the trailer that I can't get to anytime soon to measure. If you look at the camp-inn website, they must have changed the fitting at build number 758 so you would need to know your build number when ordering.
You should note that this is more than just a coupling - the left most piece is a pressure regulator to prevent damage to the trailer if the city water pressure is too high. Search for Camco 40055 water regulator. Looks like the middle piece is a garden hose to 3/4" (?) npt thread fitting and then the quick connect fitting that I don't know the size of but you should be able to source locally or Amazon.
You would be risking damaging the trailer water system if you don't use the regulator. The e-trailer site also has some info on these and sells them.
If you are not talking about the city water connection, then ignore all of this.