I've found some stuff at Benjamin Moore as far as grain fillers, sanding sealers, etc. Also make sure if you go to Canadian Tire looking for sandpaper that your looking in the right spot. Because at my Canadian Tire, theres one area with sandpaper that goes to about 800, and then (like low end fuzz said) theres the automotive section that has the finer stuff. For a long time it didn't occur to me to look in there, even though I had been in that aisle more than a couple times.
Good Luck