It is known as a Dzus fastener. They are a pain in the butt and never work.
Not listed as a separate L/R part but can be bought from fastener suppliers if you find the right size. There may be a minimum order though.
I went back and looked at your photos... so the wing snapped off the retaining post? I gotta say that is a first that I have seen. i wonder if the PO didn't know that it is not a wing bolt and that both sides of the guard need to be resting on the little plastic arms on the ceiling mounts before you tighten the retainers
This is exactly the info I needed. I'll measure the existing one and see if I can find a comparable southco part, looks like I'll have to order a few. Headed out on vacation for a week so it might be a bit before I get this sorted but I'll post back here. @rrtoadhall, it's not snapped off, maybe just a bad photo.
finally had some time to spend on this. got out the micrometer and measured the one that i had. it would appear to be a Southco 82-12-260-20 or 82-12-260-16 depending on whether you want it in stainless. Going to order some later tonight, will post back on the fit once i receive them.
There were 2 plastic washers on the one that I had so I split it up and didn't need to hunt it down at ace hardware. I can also confirm that the part number Southco 82-12-260-20 or 82-12-260-16 depending on whether you want it in stainless is the correct one. Hope that helps someone else down the road. My dog guard is installed!