Well since Fissure hasn't been a TM since the good old days of R/B/Y, there is no way to "obtain Fissure". I don't think there are any move tutors who teach this either. So you can only get it on wild Pokemon. I love Fissure too, so I'm quite annoyed when it comes to this. But some Pokemon that I like do learn it, so in a way, it's not that bad.