I am currently orbital sanding 6" DIA aluminum cylinders for paint prep. The sanding media is 80 grit max. What type of media should I specify to a prospective outside blasting vendor, and what is the best way to depict these requirements on the print?

If you need to prep without a profile then you have a rather tuff task. There is only one company that can prep without a profile.
call 330-965-0071 ask for Dean