Here is one thing that you can try. Go to Society for Creative Anachronism, Inc. and look up your nearest chapter. There will be a contact for newcomers. This is an international organization that does historical re-enactment of the middle ages. Corsets are often a part of the clothing worn for this period, and chances are that someone can put you in contact with a clothier who has experience in making and fitting corsets. In the SCA, we live this stuff, and we are real people, in all shapes and sizes. I know several people in my area who would be able to fit you with a corset. Besides this, you might find some new friends and a new hobby.