I only know of one source for chamber length gauges - Sinclair International (where I bought mine). I suspect that you may be forced to buy it from there - this tool is so specialized and cheap/low price that I suspect it would not be worth the trouble for Canadian dealers to get these (however, as I am not a dealer, I could be very wrong).
NOTE: for those who are unfamiliar with the chamber length gauge, it is simply an insert that is Flat on one end (Diameter equal to SAMMI specs) that you place into a empty case that you then chamber. This tool lets you measure the exact length of your chamber (not the headspace). Using this tool, I found my chamber to to .028" longer than the SAAMI Maximum length (I have it on good authority that it is more common than not for factory chambers to be longer than SAAMI specs .