Over at PS 63 on East Third Street between Avenue A and First Avenue...
Per the MARTE website:
MARTE (Manhattan Artisan Retail & Trade Emporium)—is a weekly upscale flea market taking place at school locations throughout Manhattan. The flea is a collaboration between each school’s Parents Association and Manhattan Media, the leading publisher of community newspapers and Manhattan lifestyle magazines. Each market is free to the public and features new and antique jewelry and furniture, local artists, food vendors, and entertainment. Proceeds from the events directly impact the schools and Parents Association.
10 a.m. to 5 p.m. every Saturday this summer. (It's also open tomorrow for the kick-off weekend.)