While at the Canadian War Museum walking down a corridor to the library and I noticed a sign on the right hand side. Go through the anteroom and you'll find a used military bookstore operated by the Friends of the Canadian War Museum. Like so many friends organisations in the heritage sector it operates without a lot of fanfare helping support the museum operations.
The store is staffed by volunteers five mornings a week. Stop by and browse for bargains if you're visiting the museum.