Hi, I would like to add that the web radio site
www.last.fm has a lot of great Mahler recordings available for full-length listening for free, even on-demand if you live in the US, UK or DE and/or as a stream in several radio stations. You could start on
Mahler's artist profile which has a "similar artists" radio button, try out the
Gustav Mahler group member radio or listen to special
tag radios which the Last.fm users have created, e.g.
Das Lied von der Erde or
Kindertotenlieder. Finding available albums with Mahler performances works best if you use the
album search and pick those with a play button which indicates playable tracks on that album.