Before you ask for a TeX macro or LaTeX class or package file to do something, try searching Graham Williams' catalogue. You can also search the catalogue over the web.
If you have learnt of a file, by some other means, that seems interesting, search a CTAN archive for it (see finding files on CTAN). For packages listed in The LaTeX Companion the file may be consulted as an alternative to searching the archive's index. It lists the current location in the archive of such files.