The cruise company web sites generally have a schedule listing the entertainers or you could simple contact the cruise director's office and make an inquiry. Similarly, if you have a particular mage you want to see, simply eMail them and ask what cruises they work and when so you can plan your schedule accordingly.
I would also contact the cruise director's office, since he is the one making the schedules for all performers. However, I'm not sure if anyone can tell you what performers will be on the ship, one year from now. First you need to know what ship you want to go to, since they choose performers that live relatively close to the home port of the ship. If you don't care which ship it is, and you are more interested in the performer, then they need to see if that ship is changing home port in that period, because if it does, than the entertainers will change too. And in the end, even if they can pinpoint the exact performer and the ship a year from now, he may still be sick that week or his flight may be canceled or late, and he won't make it to the ship. It happened more times than you think.
This may not be the answer that you were looking for, but I'm just giving you a heads up that no one can tell you 100% what performer will be where, especially a year from now. But they can still give you a ball park I guess.
