I found a lot of pattern designers listed by doing a search for "custom pattern designer" in my search box. You could try that, or look in your local yellow pages for a custom designer. Another way is to look up "custom handbags" and find out who designed them.
When I am asked to design a pattern or costume from a design concept, I generally charge between $100 - $200 an hour depending on how difficult it is, and what level of design they want (i.e. specific fabric match).