Its almost impossible to remove the inner door panels without damaging the retaining clips, rendering them unsuitable for reuse. And OEM replacements are NOT cheap.
Here is a photo of one from my S40 damaged during removal and attempted refit
I have found a source however at a very reasonable price. I picked up a bag of 25 clips for just A$33. Smaller quanties are available.
I got them from Car Parts Clips and Fasteners, Terracotta Drive, Blackburn, VICTORIA 3130, P: 03 98779999 E: sales@carpartsclipsandfasteners.com.au
In this pic left is an original clip in its compressed installed state, a new clip also compressed is in the center and an uncompressed new clip on the right. The new clips are actually intended for Audi and VW, the suppliers part number is CD0144
This image lifted from their web site