Are there any sources for body panel replacements? It's rusted out under both my tail lights and I'm starting to look around for a replacement panel section.

 

To my knowledge, mini's sold in the us had a 10 year rust perforation (rust through) warrenty....you might still be underwarrenty depending on delivery date...
Before you look to far...check with the dealer first...
A body shop might have a 3rd party scource...but a wrecked mini might be the cheapest way to get the part if a wrecking yard/recycling place is near you....