Hi,
I think you'll find that most large rodent breeders use CO2. Any other method would be too time consuming to be profittable (I know that sounds callus but it's a necessity of doing business). As well, there really is no profit in mistreating your rodents. Poorly treated animals very quickly become unhealthy and just as quickly people complain about the quality of what you're selling. The Canadian reptile community is quite small and word gets around quickly. You might want to look at the Canadian Board of Inquiry at
www.faunaclassifieds.com to see who is flagrant.
Did you post in the classifieds in the "other" section? That's where you are most likely to find a local breeder. Visit them if in doubt. Also, try replying to old ads. If they bred mice then they might still breed mice now.
Hope that helps.
Michael