Here's a list of bookstores we know are selling it:

California
• Bay Book Company, 80 North Cabrillo Hwy, Half Moon Bay (Strawflower Shopping Center)
• BookShop West Portal, 80 West Portal Ave, San Francisco, CA
• Christopher's Books, 1400 18th St (at Missouri, on Potrero Hill), San Francisco, CA
• Coastside Books, 432 Main St., Half Moon Bay
• Exploratorium Store, 3601 Lyon St, San Francisco, CA
• Gallery Bookshop &amp Bookwinkle's Children's Books, 319 Kasten Street, Mendocino, CA
• Harbor Books & Gallery, 270 Capistrano Rd., HMB (Harbor Village in Princeton),
• Ink Spell Books, 500 Purissima St., Half Moon Bay
• Out of this World, 45100 Main St, Mendocino, CA
• TechShop, 120 Independence Dr, Menlo Park, CA

Oregon
• Powell's Books, Portland, OR

Texas
• Modern Art Museum of Fort Worth, 3200 Darnell St, Fort Worth, TX

Wyoming
• Wind City Books, 152 South Center St, Casper, WY

Canada
• Octopus Books, 116 Third Ave, Ottawa, Ontario
• Mortimer Snodgrass, 56 Notre-Dame West (half-a-block from Notre-Dame Basilica), Montreal, Quebec

And, if you can't find it at your local bookstore, you can always get it on online at Maker Shed, ThinkGeek and Amazon.