For the Lower A pillar. You'll probably just have to fabricate an extension for the commercially available patch panel. Which should be pretty simple. It's essentially just a " U " with flanges. You will also probably need to fabricate the cage that holds the hinge " nut/plate " also a pretty simple thing to fabricate.
The the cowl vent box area, I'm pretty sure I've seen patch panels for.
Edit - is this the other piece your looking for ?
https://www.autometaldirect.com/lowe...-gmc-c-k-truck