The forum covers all reasonable topics related to Canadian and Commonwealth armies in the period 1900-1999.
I'm familiar with the book in question; the only time I've ever seen one was when I loaned a copy from the University of Calgary library.
Canadian military themed hardcover books of similar vintage seem to fetch 100 to 200 dollars on auction sites.
I've seen copies of especially popular vehicle books like Hunnicutt's SHERMAN go for $500 and up. Depends on the title, rarity, etc. I'm not familiar with the going rate of Gregg's work specifically but would not be surprised to see it in the $200 to $500 range.
I frequent used bookstores in Calgary fairly frequently; I will keep an eye open for a copy here and if I find one can let you know via private email.