I'm not sure that I would say the C206 is being replaced. If anything, the operators are expanding by acquiring more airvans, but the C206's are not being phased out. From my current spot in the office I can see more C206's parked on the apron than airvans.
The numbers of each type of aircraft are constantly changing, but as a rough guideline of who operates what types:
(And someone can correct me if I'm wrong here...)
Air Shakawe: C206, C207, C210
Delta Air: C206, C210, GA8
Kavango Air: C172, C206, GA8
Mack Air: C206, GA8, C208, Kodiak
Major Blue Air: C172, GA8, C208, BE58, B200, Hawker 800
Moremi Air: GA8
Safari Air: GA8, C208, Kodiak
Wilderness Air: C206, GA8, C208
Sadly, Fridge Air closed its doors in Maun last year... but I am enjoying the kitchen/ hospitality supply shop that took over their office space. You win some, you lose some.