Behl I wouldn't sweat it too much if you don't have the right rootstock. I have been told that Reticulata doesn't take on Cherimoya rootstock. Personally, I haven't had any success to report.
As far as the Ilama, I don't think that there's a lot of it available on the market right now. Excalibur is out until next year. I don't know who else has them available for sale.