you can use any buffer tube, by any manufacturer you wish. You have to use a rifle buffer in a rifle buffer tube and a carbine buffer in a carbine buffer tube though.
I think his specific question is: Are there mil spec sized buffers like there are mil spec sized receiver extensions (requiring mil spec sized stocks) or will all buffers fit commerical AND mil spec receiver extensions?
I confess I do not know the answer, but I'd like to know as well.