A portfolio will really help here. If you can put together a small site that shows what you've done before, that will help. The Drupal agencies (the better ones, anyway) will also probably want to see some activity on Drupal.org, but that's not necessarily a deal-breaker. If you do want to work on Drupal, go to some Drupal meetups, and make it your goal to be ready to apply for a Drupal job at the next DrupalCon in Austin next year (Drupal has a learning curve, you will need the time).