Looking at Pandora's rockers. The ubiquitous rust at the rear wheel wells. Seems to be limited to the rear half of the rocker panels, so I need to find a supplier for those bits. No luck in my area of Canada, (SW Ontario), so far.
Any ideas from farther afield?

 

If you're not in a rush, you could try Dave Roche, but they're quite expensive:
https://www.xk8-parts.com/?s=repair+sills

You may find further remediation work is needed once you open things up. It's worth having a look at RaceDiagnostics' and XKR-DAY's threads on this.