List RVM's known Rubies. RVM doesn't automatically know which Rubies are available out there, and may not be updated very quickly. To make sure the Ruby you want is in there, list the known Rubies and look through the list for your preferred version. You'll see that (at the time of this writing) ruby-1.9.1-p0 is listed on there. That's version 1.9.2 at patch-level zero. In other words, the first release of 1.9.2.
$ rvm list known