Since Detonics USA has announced that they're basically only making stainless guns from now on, you would likely have to get hold of an outfit that darkens stainless in one way or another, if you want the part to match your MK1. I know it can be done in a number of ways: teflon and ceramic coatings, etc. The Detonics USA pictures I've seen show that the guns have blued sights though.
...Deeton