The Mojikyo font set is the mother of all character sets: or rather, a font set. It is available free for non-commercial distribution and for a fee for commercial use, and tries to have as many variant characters as possible: the opposite approach to Unicode’s Han unification.
The Wikipedia entry for Mojikyo is sparse but OK. It also has a link to the download page at MS for GB18030 support. (GB18030 is the PRC equivalent to Unicode, or at least their equivalent to UTF-8: the encoding system is different to UTF-8 but byte based, and the code points are different to Unicode, but transcodable.)