Hit a snag with my Prop valve/line

No that is a proprietary piece, part of the valve, and never available separately. You will have to find another valve, junk or otherwise.

I BELIEVE you will find that the flare nut you hold (on the line) in the photo is the wrong size nut. That is NOT a "standard" size nut for that size line. All manufacturers used "non standard" flare nuts on brake lines (especially master cylinders) to make sure the lines got installed in the correct places, IE impossible to switch the front // rear master lines

GOOD hose/ fittings/ parts suppliers do have adapters up/ down in size if needed. This used to be common when installing hydraulic trailer controllers