When trying metric_fu, gem told me quite gently, though persistently, that it did not know about metric_fu. Blimey. You’ve got to look around the Intarnetz, but then you can find the stuff you need to get more than one repository.
So, what’s the trick?
lists the sources that are already available.
gem sources -a http://gems.github.com
adds that source to the other sources. Jay! That’s what we needed,