You can't find who voiced Alistair Alphabelly anywhere on the internet!
Robert Martin Klien is listed as the voice for Alphabelly on FandomWiki and in the credits of the movie. Originally listed was Ryan Seacrest as "Allstar Alphaberry" rather than Allister Alphabelly. As the actor now goes by R. Martin Klien rather than Robert, we were able to update the true actor for plays Allister Alphabelly.