A couple of people saw my new Greenland paddles in my car recently and asked what they were. Until a couple of weeks ago I had never paddled or rolled using one. But I went wild on my trip to Michigan and bought three different Greenland style paddles.
Betsie Bay Kayak is one of the few companies that I have ever found that has had any in stock, I purchased the Greenlander, Storm and Rolling Stick, here are the descriptions from the Betsie Bay website:
A small hand-paddle based on the shape of the Inuit atatl (spear throwing stick), which could be used for rolling if the paddle was lost in a capsize. It is an excellent tool for learning the Greenland hand roll.

I have used the Greenlander and the Storm, I watched a few videos of the slide stroke prior to using the Storm, holly cow was it tough at first, but after ten minutes I got into the rhythm.