Hello,
There is 2 that I know of.
1. At the French International school near Giang Vo. They offer classes after school. Sorry I don't remember the schedule so call the school and ask them, I think their info is somewhere on here.
2. Trung the thao 10-10. This is a Vietnamese type community center with soccer fields also. The instructor is really nice and speaks good English, but really if you just follow everyone else you will be ok in class.
If my memory is correct the price was about 250 000 VND for 3 months so you cannot beat the price, and the classes are Tuesday and Thursday 6-8 pm.
You will need to buy a GI and there are a bunch of shops near the stadium who sell equipment and GI's, I would suggest a thin one since the summer and there is no A/C at the Vietnamese one (no sure about the French school).
Overall its a great experience anyway and I really miss my training there, but unfortunately new new schedule doesn't allow for much training.