This is a great article to refer to explaining cultured Japanese pearls versus Chinese pearls:
http://www.pearl-guide.com/japanese-akoya-pearls.htm
Chinese pearls are taking over in all aspects, including quality and price. Although larger Akoya pearls are predominantly from Japan at this time, the trends are changing and the Chinese pearl farmers are perfecting their techniques for producing high quality Akoyas in all sizes.
It's amazing how fast this change has occurred, and this is a big indicator that the Chinese pearl market will continue to strengthen. Unfortunately, many retailers are not aware that the pearls they are selling are, in fact, Chinese.