If you are in a large city you may have a fastener distributor there.
Lookup fasteners in the yellow pages and call them, you are looking for a blind nut, there are many different types, and a well stocked trained supplier will be able to locate exactly what you need.
Here is one near here, if they do not have anything you are out of luck.
MidValley Distributers (
www.midvalleydist.com/)