My cargo EB is missing some factory plastic interior door panels. I've had little to no luck finding any panels. Specifically the RH cargo door and both rear doors.
Are you referring to the plain black plastic ones? If you want them I will sell you mine for cheap. I am going to swap all mine out for the aluminum ones.
You could look on eBay but be prepared to pay upwards of $150 each, shipping all over the map due their physical size.
Another source I've found to be very good is LKQ---they have a number of regional locations as well as an online presence. If parts are available out of your local area they can ship direct or have them transferred closer if you'd like to inspect in person before purchasing.
Saline, have you checked with FamVans? Aren't they the ones that have the huge selection of van parts? If not that I would take a day trip to Denver and hit all the PullaPart yards.