If you lay out the specs., provide a drawing, and supply the type of material you want, any tailor with a heavy duty sewing machine should be able to do a soft case for you.
If you are talking hard cases, setup & tooling is going to make a one-off case extremely expensive. For a hard case it would be better to buy a case the size you want and then subdivide it with spacing bars.
Good luck!
Bountyhunter