Sheet music (object)

I know that "sheet music" denotes printed music (as opposed to recorded music), and that it is an uncountable noun. Very often, when talking about pop music, it's used to describe these thin, often 4-page booklets with the piano score and guitar chords for a song. When you want to buy such a thing you see ads with a title like "'She Loves You' Beatles sheet music". So, if I decide to buy, say, three of these items, how should I say so? I can't say "I've bought three sheet musics" (not even "I've bought three sheets of music, which is not necessarily the same), since I understand that "sheet music" denotes what is printed in that paper, not the paper itself. How do you call that thing, then?