For anyone looking for dzus to fasten rear window louvers to the brackets, I found a source.

Part Number is PAN-B5400 from PanelFast.
Description is "5/16" allen oval head with 0.400" grip"
You can buy then here or here.
They come in plain steel, so pain or powder coat to make them pretty.

The allen is 3/16", which is slightly larger than the factory allen/dzus.

Bryke Racing has some, as well. They're slotted, not hex, though:
https://bryke.com/quarterturn-button...um-5-16-black/

You need the .400 size (102-213bk)