To be perfectly honest with you, most catfish if chosen correctly are suitable for the mbuna tank. When i set up my first african tank i added synos first but with later experience i learned its not as essential. The only exception to this rule is if you intend to house the cats with an exrtremely large and aggressive cichlid such as a frontosa who would see the new cat as an intruder!
Yes i have mbuna multiple mix, and i also have a whole host of other catfish mixed in, try any of these species:
Doradids (raphael cats)
Synos, suggestions are multiplepunctatus, ornataqpinnis, nigriventis, ocellifer and flavatus
Plecos, provided they are not overly territorial such as peckolita taparas, or flimsy such as whiptails
even some of the smaller mystus and pimelodae species are nice, try pim pictus!