You can just go buy the CD, load up the WAV files and mess with them.
Seriously, there are too many CD's where the sound is totaly wrecked in the mastering process, unfortunately. Comon malpractice like excessive compression or clipped samples.
Infamous examples include Red Hot Chili Pepper's "Californication" which is excessively overdriven and thus clipped, ie. RMS = -5 dBFS sine. The album "By The Way" is slightly softer, about -7 dBFS RMS sine, though multiband compressor on this sounds even more evil than the worse radio stations. (btw. my signature explains this issue with a demo!)
I did several remasters myself, also private use only. The sources vary.
If you're lucky, you can get hands on a good studio bootleg. For example, there is one around from that "Californication" album, not excellent, but much better a source than a ripped CD nevertheless.
Here is an example of it:
http://www.abmischung.de/mixdemo_RHCP_-_Around_The_World.ogg
Another remix from a studio bootleg in Dolby Prologic:
http://www.abmischung.de/mixdemo_Kraftwerk_-_Autobahn.ogg
Also 5.1 surround DVD tracks can be a good source for a CD remix/remaster. A comparative example, first you hear a regular downmix, after that the remixed and remastered version:
http://www.abmischung.de/dregs.ogg
And yet another example from a DVD source:
http://www.abmischung.de/mixdemo_Rosenstolz_-_Eine_Frage_des_Lichts.ogg
Sometimes, the vinyl record got a way better mastering than the CD version, thus restoring from vinyl can be worth the effort.
Also here I have an example:
http://www.abmischung.de/mixdemo_RHCP_-_Dani_California.ogg
And eventhough ripped CD tracks are usually a cosiderably bad source like I said, there are exceptions to this, ie. the ABBA gold seems to be sampled directly from the master tape including all dropouts etc. Absolutely no restauration, compression, EQ'ing, no anything seems to be done to it, yet it is still the best version of the ABBA hits around. It was a great source for a remastered. Here is an example:
http://www.abmischung.de/mixdemo_ABBA_-_Super_Trouper.ogg
Also note that all my examples have a total RMS of -14 dBFS sine, which works quite well with most genres.