roygpa, The fabric used to cover cases is 1000 denier nylon or polyester. Cordura nylon being on the expensive side and polyester being the least expensive. You probably won't notice much difference and many inexpensive cases are made with polyester. There's not a lot of people that buy from fabric stores like Jo-Ann Fabrics that would have a use for this type of fabric nor would their machines handle it well so I don't think you'll find it there. I do know of some people that have used home type sewing machines to work with this fabric but an industrial will handle it better.
Do a Google search for 1000 denier fabric and you will find sources.