Shern - It appears that Pelican Parts just ran out of stock and the supplier no longer makes it. If you go to PP it will allow you to add the item to your cart, but your order will be cancelled - I spoke to someone at the parts warehouse and they said it's no longer available. I've been checking ebay but nothing has popped up.

Not having a lot of luck with junk yards, many places refuse to do anything with brake or vacuum lines 🤷

Diesel 911- thanks for the tip. I may end up doing that. I wonder if anyone knows the pressure differential spec for the check valve - or is it pretty standard? Something like this seems like it might work - Aluminum One-Way Check Valve 12mm Barbed - it says it holds 90 PSI.