I do custom made, via mail order, all the time. I get requests for this service from all over the world. It is not a simple process and requires work on the clients part as well. It entails a pretty detailed list of measurements needed from the client (supplied with an equally detailed set of instructions).
It can be filled out by the client, with help of a friend or tailor, and I make myself available to help via e-mail or phone. I make mostly pants this way. I have done much more complicated pieces like Catsuits and Jackets via the mail, but I want at very least one in-person fitting on these types of projects!
When clients see the chart, many US clients, in their initial panic upon seeing it (Pl-eeze, it is 2 pages including instructions!) is: "But my my jeans size is______"
The answer to that one is HERE. Courtesy of Esquire's Excellent Style Blog.
It should be required reading. It is true for both Men's & Women's jeans.