I used the Unix "locate" command-line tool. I just searched for "keybase". Note that you have to build up a locate DB first by calling "sudo /usr/libexec/locate.updatedb". Type "man locate" in Terminal to learn more.
Note you can also use 'mdfind' for this (assuming you haven't disabled Spotlight), no need to build the updatedb. I actually have locate aliased to mdfind in my bashrc.
For those who are curious: To be accurate, locate is a command provided by mlocate package (shipped by most modern distributions) which supersedes GNU slocate.
mlocate is a locate/updatedb implementation. The 'm' stands for "merging": updatedb reuses the existing database to avoid rereading most of the file system, which makes updatedb faster and does not trash the system caches as much.
The locate(1) utility is intended to be completely compatible to slocate. It also attempts to be compatible to GNU locate, when it does not conflict with slocate compatibility.