This link will tell you if the Duo! book is available.
This link will search Prospector for additional books of duos (also called dialogues) -- remember that it takes 3 to 4 days to get books through this system, and pay attention to the year of publication -- there are some OLD dialogues out there...
Most of the scripts/scenes available online are either in the public domain beacuse they're old or have been posted by the author because they're unproduced and the author wants some publicity. In the case of the former, they might be too dated for class. As for the latter, the writing may not be at professional level. Still, you may find something, so there they are.