In my neck of the woods (NAmer) I've only ever heard M.A. in. The reason is that M.A. is usually expanded in English as Master of Arts, and Master of Arts of Information Science or Master of Arts of Philosophy is wrong, because the second thing is part of the first (philosophy is part of the arts) and not the other way around.
It all gets pretty complicated pretty quickly. Philosophy is actually more in the humanities than in the arts, but you can't even say 'philosophy is a humanity', because humanity is never singular in that sense.
My advice is to stick to the standard jargon, which is 'in.'