I just used a normal U-bolt available at any hardware store. Then I painted mine black. They work great. I've had them for about a year, and haven't had to repaint them yet to due scuffs from removing and inserting the gun, although at some point down the line, I might need to do that. But, obviously, repainting is very easy to do.
The first picture is just of the U-bolts, I'm referring to. They're availble in a large number of sizes.
Then the other two pictures are of my cabinet with the holders. I couldn't find a better view than that, sorry.