I really does not know if this is about searching for a free software
replacement for iTunes on Trisquel, on the way one should buy music, so I'll
try to answer both.
First, the closest FLOSS iTunes replacement I am aware of is called
Nightingale, which is a fork of Songbird, made of a frustration that the
original developers stopped supporting/providing GNU/Linux builds. Also,
Nightingale does not come with any proprietary parts, that SongBird will ship
by default, including addons, with are AFAIK free too.
For buying music, there are many ways of doing so, including, but not limited
to buying CDDAs, Vinyls (for exceptional audio quality), and FLAC encodings.
I personally does not buy music since the albums I usually want are not
available anywhere, so I am downloading them using the Internet (legal in
some parts of the world, including the one I live). My favourite website of
doing so is RuTracker.org where these albums are usually available.
