The big studios for classes are:
http://www.broadwaydancecenter.com/schedule/schedule_hiphop.shtml There is house, vogue, locking, waacking here, though the schedule and teachers change over time.
Because this is a more commercial studio, most "hiphop" classes are going to be street-jazz brand of hiphop, not old-school/middle-school hiphop. Research the teachers! Ephrat, Ms Vee, and Eric Negron may be good places to look for old-school hiphop styles. While Luam and Rhapsody may be what you want for the commercial side (more street-jazz, la-style, etc).
http://www.peridance.com/openclasses.cfm Be sure to check both Hiphop and House sections!
Sometimes many OGs may organize classes on their own, and book a studio. Buddha Stretch, Ejoe, etc. You have to pay attention to their facebook pages and pay attention on facebook, as you may often only get less than one week's notice.
You may find special classes/workshops listed on http://www.dancedeets.com/?location=NYC as well, for both commercial and underground side of things.
Tony McGregor also has a self-organized weekly class: Ripley Grier Studios 500 8th Ave (between 35th and 36th street) Monday 9-10:30pm-ish $20 per person More Info: https://www.facebook.com/events/648998528469293