I saw them at IKEA, though I don`t know if they have magnetic sides or not. They also have those big roles of paper that you attach to the easel and just rip it off when you`re done. You can check their catalogue online.
We have the Ikea one. Bought it because it is stand alone/tall; most of the others we saw would need to be put on a table.
It has a black chalkboard, a dry erase board plus the big roll of paper.
Not magnetic, just checked.