I've been trying to find places in Beijing to take up a Martial Art, so I'll share what I've found so far:
Black Tiger/Club Hero have an awesome gym and they teach Muay Thai and Brazilian Jiu-Jutsu. It's pretty expensive though at 1000RMB a month, and I couldn't justify joining as I'd only be able to come to classes once a week.
Art of War run classes but I think I was discouraged when I found out it's pretty far away from Chaoyang district around by the Olympic Stadium, I think. This might be fine for you, I just didn't look into it because I'd be coming in from Yan-Jiao anyway so
wanted somewhere close to Dawanglu/Guomao subway stop.
http://www.bjjchina.com/en/?q=node/13 looks decent.
But yeah, I haven't found any Judo places specifically as it's not really my thing.