Getting back into it. Tips/tricks for finding stock?

Hey there so 151 gave me the itch and I'm getting back into this cardboard crack, are there any tips/tricks for findings stock/restock dates etc. for 151? I'm in Canada and Costco has a relatively absurd amount of UPC 's but in terms of booster boxes etc., any help where and when to look for that would be great! (picked up two UPC's to start)