I still haven't found a public source for the gem, but I did manage to copy it from the snowflake server to my workstation. I had to copy a directory and a configuration file:
~/.rvm/gems/ruby-1.8.6-p420/gems/activerecord-oracle-adapter-1.0.0.9250
~/.rvm/gems/ruby-1.8.6-p420/specifications/activerecord-oracle-adapter-1.0.0.9250.gemspec