How many season are there in clannad anime?

Not likely, the visual novel of the same name in which Clannad was adapted from ended where the second season left. The only way there would ever be another season would be if they adapted Tomoyo After, but is still wouldn't be the same because it does not follow the original story at all.

I was a bit sad as well to realize that there would be no more Clannad, but you could always play the visual-novel (there was a English patch released by some nice fan-subbers), which has more story than the anime adaption had ( I haven't played it yet, but I read something where some guy said that there was 200+ hours of character development). You could also play Tomoyo After (there has yet to be an English patch released, although Doki fansubs is currently working on it), but be wary, it doesn't follow the original story and is a for ages 18+ game (features scenes of a sexual nature).