Thought this info might be useful to other folks, as I had a bunch of nicks and scratches on my Bruniton coated M9 slide that I wanted to touch up but couldn't find a lot of info on repairing them.

My understanding is that the Bruniton is an epoxy-based finish over parkerization.  Epoxy paint was surprisingly hard to find, but I found some VHT Epoxy All Weather Paint.  This is an automotive paint so many auto parts stores carry it.  I got the satin black.

http://www.vhtpaint.com/products/epoxypaint/

First I cleaned the scratches with some finish safe gun cleaner.  The paint only comes in a spray can, but I just sprayed it on some plastic and then used a small brush and toothpick to fill in the scratches (all that plastic model experience from years ago really helped).  I let it dry for a few days, then GENTLY buffed using a cotton tip on a Dremel tool with a touch of plastic polish to blend it in a bit.

Not saying it's 100%, but it hid the scratches pretty well, and the epoxy paint should be a lot more heat and chemical resistant than normal touch up paint.  I'm quite happy but no guarantees on this, so if you want to try it test on a hidden area first to make sure you're happy with it!

Hope this helps.