Go to your local feed and seed store for new flats with cups or try WAL-MART, HOMEDEPOT OR LOWES sometime they just throw them away after the plants are sold. Hope you find them.

If you don't mind using used flats and pots, local ladnscaping companies are a great source for them. When I see their trucks and trailers at hotels or parks working, I always stop and ask for the flats and pots when they are finished. Last fall I got about 30 or 40 flats in one stop.
Jim