Re: Glock 21c , trying to figure out where the slide came from ? !!
GT Distributors has a place in florida that they send their factory turn in guns to do this. NiB is what they call it - I think...for Nickel Boron. They charge $70 or $80 over the cost of a regular Glock to do it.
I have heard nothing bad about the finish as it pretty much makes the gun rust proof 100% and seems to wear very well...tough stuff.