Just get a 1/2" Sharkbite shutoff valve or equilalent brand ... cut the ends of your 1/2" water line square and push it on. Or try another RV dealer. I always carry 1/2" Sharkbite union and plug fittings along for this very reason.
Or ... just order one like you have online.
https://www.amazon.com/RV-Fresh-Plum.../dp/B01F18KPIM