Did you try Frankies?

Here is a link that might be useful: frankiesnursery.com/

I read that the Atemoya is a cross between a sugar apple and a Cherimoya. Because it is a hybrid it won't come true to seed. I suspect you have a sugar apple if you are at low elevation. Cherimoyas do better at high elevation. The advantage of the hybrid Atemoya is that it is as tasty as Cherimoya, but does well at low elevation.