I’ve been using a laser cutting service for some projects at work recently.
If you could get a CAD file drawn up using the stub of the heat shield you have, you could at least get a quote for having a flat cut.
You’d need to find a way to bend it round though.

I could do the CAD file for you but I’d need the heat shield in hand.

Anyway, the cutting service is Online Laser and CNC cutting for metals and plastics - Instant Quotes