Only 12 stores are participating, including some in Colorado, Florida, Michigan and New York. You can find the full list here. The number of workshops also varies from store to store. For example, Colorado's Flatiron Crossing Apple Store has just one, 90-minute workshop listed, while New York City's Upper West Side store lists six over four days.
Unfortunately, I'm out of luck here in Massachusetts as there aren't any listed. Selections probably depended on each store's typical traffic and number of trained staff, among other things. If you're lucky enough to attend one of these, have fun and let us now how it goes.