if it were in season you can order it from cherimoya.com it's usually available in the fall. I was able to find it at an asian grocery in chinatown in Philadelphia. it was $6 for 1 fruit.
it is an expensive fruit, but suppose to be excellent flavor, however the ones I bought from the store didn't have a flavor. Fruits directly from the farm would be picked at peak flavor.
I have few pitayas growing in containers in my greenhouse. they won't flower until later on.

Bass