The "Official List of Casualties to Members of the Canadian Expeditionary Force" was a publication of the Canadian Ministry of Militia from1915 to1918. It is now a rare find. The only copies I have been able to locate are in the Regional Room of the London, Ontario, Public Library. The Regional Room's collection unfortunately is not complete. They have volumes 1-8, 14, and 16-18.
As my interest is in the battalions that came from Southwestern Ontario I will try to scan for those battalions. The year 1915 for the 18th. Battalion is below. It will take a while to do the 1st. Battalion as there are over 30 sheets of casualties recorded through 1915 alone.
The first page is to June, 1915. The second page is from October 1 to December 31, 1915.