there are 2 options that i have found
#1 - buy from
The Source their brand of duster
http://www.thesourcecc.com/estore/Pr...roduct=6404350
#2 - buy
MG Chemicals Super Duster 134a
http://www.mgchemicals.com/products/402a.html
i would go with MG duster since it is cheaper. check out their website for Canadian distributors in your province.
tetrafluoroethane (134a) = safe to use in your GBB (make sure to still use silicone oil)
difluoroethane (152a) = bad for your GBB