You can probably get just about any trim piece at the yard.
Some specific leaks to look for are the top corner of the door seal. They tend to shrink and leave gaps. And the sunroof drains can get clogged or disconnected. If you open the roof and slowly put water in the inside area and no water goes away, they are clogged. If the water does drain, but no water drips from the wheel wells where the drains dump, they're probably disconnected and draining into the cabin. They frequently require the headliner be dropped to reconnect them.