I do not currently live in Canada. There are four dollar stores within ten minutes of where I am living now, and none of them sell resistors, switches, audio jacks, etc. I have purchased MANY earbud headphones from dollar stores and they all have been crap.
Either way, RadioShack is the only store near me that sells the parts that I need, and I get a deep discount because I work there. Additionally, every dollar store I know of--they do not take back returns. RadioShack does. Anything I don't use I can exchange for something I need.
Do you have Wal-Mart stores in Canada?