As far as I know, there are some fruit wholesale markets and shops near Fushui Dashi Gymnasium in Quanzhou, Fujian. You can try to buy watermelons wholesale in these places:

Dashi Youth Farmers' Market: This market is located at No.25 Sunshine Street, Dashi Village, Feishui, Quanzhou, near Dashi Gymnasium. The market mainly sells fruits, and many merchants can wholesale watermelons.

Lishui Vegetable Wholesale Market: This market is located at No.0/2, Fu Lin Road, Feishui, Quanzhou, not far from Dashi Gymnasium, and many merchants sell fruits.

Chongwu Fruit and Vegetable Market: This market is located in Chongwu District, Quanzhou City, near Feishui. Besides vegetables and fruits, there are other daily necessities. You can go to this market to wholesale watermelons.

I hope the above information is helpful to you. Please pay attention to the selection of regular merchants and suppliers during the purchase process to ensure the quality and safety of the purchased goods.