Not hard to make a faceplate or side mounting tabs/plates for an A2000 to fit into a standard rack. I suppose it's a possibility some company made just rack adapters for the A2000, but they weren't terribly hard to make with a few scraps of sheet metal. The matching color is a nice, clean touch though.
Did it myself years and years ago when I was still running a BBS on legacy hardware - the dimensions on an A2000 case are just perfect for mounting in a standard 19" rack.