http://www.uline.ca/ needs you to buy volume.. but you could always split it with someone. too bad you're on Montreal .. if you were in T.O. we could just go halves on some of it.
Most of what I get comes from retail locations near me who are more then happy to dispose of it without it eating into their garbage limits.
I just ask retailers to save me the popcorn and boxes and I go by about once a week to pickup or so.