If I remember my history well, slave trade in East Africa was chiefly conducted by Arab traders. Zanzibar was major slave market, and many enslaved East Africans either ended up in Arab countries, or in the West. Check out the book Wretched Africans by Joe Khamisi. Regarding conversations around slavery in Kenya, I can't say this is something that is often discussed in the public space. In general, we Kenyans have a (unconscious) preference for amnesia when it comes to difficult historical issues.