It's going to difficult to get an exact match, heat resistant paints are mixed at the factory and to get an exact match would require buying a lot of different colors of that particular paint and lots of mixing to match a color.
You might get lucky and find one that matches at VHT:
http://www.vhtpaint.com/products/flameproof/

Yeah, I figured it was a long shot.
Have you tried checking your local home improvement store?
A quick check at Lowe's online and I found a few high temp paints in 1gal jugs, they might be able to color match if they have the necessary paints, but that's likely a long shot too.