Lovin Fish
Aquarium Advice Freak
I have 7 of them in a 55 gallon with a 20 gallon sump and a RIO 2500 pump. You dont think that is 2 many do you???
I don't have experience with Mbuna tanks (love them though!) so I did a quick search for you to get a rough answer...here it is.
For the most part, it depends on what species you have and the ratio male:female. From what I found, if you research your species choices, you will be able to achieve a balance allowing you to stock 8-16 which is a wide girth between the numbers. One thing I have read over and over about stocking a Mbuna Tank is that it is important to stock them all at once because of the aggression level. They will fare better together if they grow up together.
Anyhow, at least that's a tid bit of info. As Heather suggested, the cichlid section would be your bgest bet!