If you happen to know what company made the chairs, ctc them for help. If you don't, perhaps when the 'new line' of patio furniture hits the stores, you can look around in a few stores for similar chairs, and call THAT company.
At worst, there are kits for re-doing patio chairs and such. The kits may not be the same as what you had but it may be best to bring a chair with you to see if the kit(s) you find can be used on your chairs. As for where to go, I could tell you if you lived in SE PA. But my $$$ says you don't so perhaps you can start with Swimming Pool places. Even a Furniture Repair Shop may be able to point you in the right direction.