If you're keeping your mbunas in the relatively hard, alkaline water that they prefer then your options are going to be a bit limited. There are some Mastacembelid eels (African relatives of the Asian peacock eel) that are native to the African Rift Lakes and so will be able to tolerate the water conditions. Like many of the Mastacembelid eels, however, they do get quite large as adults (up to 36 inches or a bit more for some species). They're also pretty tough to find at your local pet store, though they might be able to special-order some for you.
There are also quite a few Synodontis catfish that are native to the Rift Lakes that will enjoy hard, alkaline water. A little research should give you some of the specific types.
Most of the other fish you mentioned in your question prefer slightly acid to slightly alkaline water and won't do as well in a tank specifically set up for mbunas.
Can you provide any information regarding the pH and hardness of the water in your mbuna tank?
-Joe