We mostly cannot buy grade B commercially, but I suspect the stuff I buy (or, often, am given) from a local farmer would be grade B or lower. Its variable, but often a bit dark .
I'm not sure who grades maple syrup with As and Bs, but here are the Ontario rules: http://www.ontariomaple.com/pages/maple_syrup_grades/ And I think you will find that as you go to darker grades, it is less suitable as a table syrup and more suitable for cooking (stronger taste).
I bought a nice bottle of upstate New York Maple Syrup at a local winery last week. Ironically, the New York Post just had an article on New York Maple Syrup and the one I bought was mentioned. I also had it with pancakes this morning. For the record, it was "Grade A" should anyone want to know.
is the most popular, with a light maple flavor and a relatively thin consistency. It’s a good choice for pancakes, and can make a great topping for desserts and other foods. Grade A is usually made from the maple sap collected at the beginning of the mapling season.
Grade B maple syrup is much darker and has a stronger flavor. It also is a bit thicker, tending towards the consistency of pancake syrup rather than the runnier Grade A. Grade B is often recommended for baking because its stronger flavor comes through more readily, but it can be a better choice for pancakes or waffles than Grade A if you, like me, are a fan of the flavor of maple in general. The two are interchangeable as far as what will work in a recipe that calls for maple syrup. For those of you looking for Grade C maple syrup, it is now called Grade B. In other words, Grade B & C are the same.