HELP water line fillings and "locking ring" needed

When I purchase my newer TAB 320 the seller discovered cracking in the flooring and decided at his own expense to replace it and in doing so the RV dealer discovered the top layer of plywood on the interior was in bad shape. My first concern was the Alde fluid or unit had leaked. But I found no real evidence of that. What I finally found while tracing water lines was an elbow fitting inside the kitchen cabinet area where an elbow was loose an basically came apart and the fitting didnot have a locking ring on it. There was no damage under the fitting but damage and water moved for near the Alde and between the Alde and the bathroom and into the plywood to the center of the floor. My guess was in talking to the owner is that last winter was colder than normal, he had only minimally drained the system and there was enough water left to freeze freeze in the are of the fitting and force it part. It didn't appear seperated when I found it but the locking ring was missing and it was loos enough that water could have escaped.

All that brings me to where am I able to buy these fitting so I can replace the fitting, lock it in place and test my water system?