How many baduk kisei (sages) are there?

I only know of Go seigen and Cho Chikun.

There’s some useful information on this page that may answer your question:
According to this source, before the first Kisei Go Tournament in 1976 "the term Kisei was conferred in Japan on only three players: Honinbo Dosaku, Honinbo Jowa and Honinbo Shusaku."
It’s also worth noting that the term “Honorary Kisei is given to those players who have previously won the Kisei title five years in a row. Currently, this includes Fujisawa Hideyuki and Kobayashi Koichi.” Apparently, if Iyama Yuta wins the title in 2017, he will also be one of the Honorary Kisei.

Kisei sounds like the highest honor to me, like literally, a sage