The majority of shoppers drugmarts have pg. They just don't want to give it to you. Just like Technobob said:
You either gotta catch them off guard and know what your talking about, or say it's for something else.
I went into 2 and asked. They kinda stumbled for a bit as i continued to ask and they came up with no we don't have it.
I tried another at Albion&Islington in toronto and there was a younger girl working. Asked her for it and she got confused. Told her i needed PG, propylene glycol and wrote it down in front of her. The other girl came by and before she got close I said "I need pg, usp grade, the other girl said you don't have it so I'd like to special order it". She walked off and grabbed it from the back.
Basically, don't look like your more clueless than them and be stern with getting your "moisturizer" base.