When PEAR installs a package it stores them in a dir similar to /usr/local/lib/php/ (on FreeBSD), but the exact path depends on your operatingsystem and/or your installation. The file you're looking for, with the File_Find object, is called Find.php. Do a search on your harddrive and you'll probably be able to figure out which one it is.. 🙂
Good luck,
Olle