I use google cuz its the best search engine en everyone can acces .
The easiest search quote is "index of ..."
Some kind of examples are:
index of ftp/ +mp3
index of ftp/ +divx
index of ftp/ +"whateveryouwant"
Google has many operators that should help you to specify your search
There are also lots of advanced operators available
here are a few:
allintitle: "index of ftp/mp3"
try to combine things and maybe u'll find something