Well here are a few links to Kenyan air charter companies that I found and checked. Although I've already wrote earlier here and here that obtaining the Kenyan permits is a pain in the ass it might worth a check. And the scenery and flying is worth everything.
Manda Bay Air Charters And Scenic Flights: www.mandabay.com/air-
Tropic Air: www.tropicairkenya.com/
Yellow Wings: www.yellowwings.com/
Boskovic Air Charters: www.
East African Air Charters: eaaircharters.co.ke
And probably the best place to start is Aero Club of East Africa (Wilson Airport, Nairobi, Kenya): www.aeroclubea.net/
All pictures: Christian Strebel, Yellow Wings