Please specify a location in /usr/share/doc/ if possible.
It's from the blt package. Unless Ubuntu has drifted far from its Debian roots, the copyright file will therefore be at /usr/share/doc/blt/copyright. It is also online at http://changelogs.ubuntu.com/changelogs/pool/main/b/blt/blt_2.4z-4.2/blt.copyright.