Brownells sells oven cure finishes and one of the colors is "stainless steel gray". The description says it's supposed to be a very good match for bead blasted matte stainless guns, hence the name. Might be worth a look, and it's only about $15 a can.
http://www.brownells.com/aspx/NS/sto...KING%20LACQUER
Dura Coat might be another option if you aren't opposed to a coating type finish. Through experience I can tell you the Duracoat is more durable, but a little more involved to apply. Not difficult though. If you call Lauer directly you might get a decent color match right off the bat. They offer MANY colors.
http://www.lauerweaponry.com/