Chinese streetwalkers can be found a lot of places, Ueno, Yushima, Okachimachi, Kinshicho,Kanda, Roppongi (used to be, not been in awhile)
Some things to be aware of:
1) Usually they will bring you to a massage shop and the girl will be different
2) Always negotiate the price and service first, 10,000yen FS, you may need to walk away and have them call you back.
3) Set the rules, make sure you specify how long, if kissing is allowed, that you are only taking a look and no money is handed over before seeing the girl or line up of girls.
4) These are normally just 1 pop service
Service will vary but if you follow the above at least you will see the girl before money is handed over.