That belt is called a "Sam Browne" belt. You can actually get one here if you don't want to make it. http://www.sportsmansguide.com/net/c....aspx?a=612615
Or you can google "sam browne" and find them in other places.
I tried to edit this before...
If you want to make it yourself, you'll need to use D-rings (I can show you what the parts of it look like) and straps, and such, which you can get from a place like tandy leather or other leather/saddlery goods suppliers.
Unfortunately, there's not a real easy/cheap solution when it comes to making one, unless you know where to get old leather parts on the cheap.