Has anyone ever seen these type of PEX connections? I can't find them anywhere online or otherwise.
These are actualy "Qest" (pronounced "quest") brand fittings that were more popular 10-15 years ago (maybe further back). I remember in the early 2000's these were sold at Home Depot and Lowes back before they had very much PEX plumbing supplies. They were common in mobile homes.
Here is a sample at a plumbing supply retailer:
It is a PEX plastic flare compression fitting.
Not an endorsement just a link: Plastic PEX Compression Flare Fitting