The gas door is listed here:
https://www.trademotion.com/partloca...15&catalogid=2
for $66.00.

As for the quarter panel, you'll most likely need a recycler. There's at least two on the site, and I'm certain that they can help you out.
If Merlin doesn't have a quarter panel, that means Isuzu doesn't have one either. Not surprising when you consider the fact that the stamping dies for the VX's body panels were only supposed to last for 5000 units.