Dan Akroyd plays a
Hohner Special 20, a variation on the Marine Band model.
The specific tone comes from it having a plastic block rather than wood.
See this link for Hohner: http://www.hohnerusa.com/
Edit -
Here's the link for the particular model: http://hohnerusa.com/index.php?8
Note that it comes in a highly varied array of keys and I've yet to find what key Elwood played.
But at least I knew which brand/model it was!

Hope that helps