When I'm looking for a footprint (or something else) in the libraries, I found that it is much faster to open a console (terminal) in the library directory and enter the following command:
grep -i so8 *.lbr
This will show which libraries contain the string so8 or SO8.
Ofcourse, this only works from Eagle version 6.xx and up which stores the libraries in XML.
In the unfortunate case that you have been forced to use the windows OS, grep is not installed by default.
In that case you can download it here: Grep for Windows
Have a nice day,