The best polyester threads in the world are Mettler and Gütermann, both German-made. There are many North American sellers on eBay selling both. Coats & Clark (a U.S. company) also sells decent sewing threads, but nothing like the absolutely consistent and dependable quality of the German-made threads.
I would never advise buying thread from China or India, especially if you're sewing garments using a sewing machine. Poor quality control and/or outdated machinery in India, combined with dubiously sourced raw product (polyester is made from petroleum products, in case you didn't know) means that much of the thread sold there is of inconsistent quality at best. At worst, it will bind, break, fray and jam in your sewing machine.
The problem with Chinese-made thread is similar, but not so much due to outdated machinery as to caliber of raw product and lack of end control of quality, as well as fake products (names close to, or mimicking well-known European or American brands, but of really inferior quality).
With both countries, you have the seller issues to deal with as well, as 'mjwl' pointed out.
Do yourself a favour -- pay a few dollars more and get the real thing. If you need a lot of thread for industrial-scale sewing, you'll find some U.S. sellers with whole boxes full of Gütermann polyester sewing thread, in a mix of every imaginable colour.
P.S. If you're doing fine heirloom sewing, there are also good quality, European-made silk and pima cotton threads available on eBay.
