First, if you're looking for a local retailer who carries the graphic novel, please click here to see a list of stores. You can also use the Comic Shop Locator Service to inquire with other stores. Most retailers can easily special order the book through Ingram Book Company if they aren't actually carrying it, so please don't hesitate to ask your local retailer to do this. They'll need the ISBN (it's 978-0-9781237-0-3), but to make this whole process a little easier I've created a simple order form that you can download, print, fill out and then present to your retailer.
Alternatively, you can purchase a copy online quite easily. A link to purchasing on Barnes & Noble is here and Chapters/Indigo can be found here. The links to both Amazon and IndieBound are below: