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Hellom, The piece behind the door is the B pillar trim panel. The piece from the A to B pillar the holds the headliner is the headliner trim panel.
eBay and car-part.com are two good sources to find trim pieces. Tan or "saddle" as GM called it was a pretty popular color so it shouldn't be to hard to find the pieces you need.
Crutchfield used to carry upgraded and paintable kick panels that would hold larger speakers, I'm not sure if they still do.
If I can help with anything else regarding this just reply back.