I'm leveling up a balance and in mushoo during my last two level increases I found a whopping total of only two food items. I find it a bit appalling that you can level at mid-upper levels and wind up training your pet without any food in your inventory cause food drops have been that scarce.
I've noticed that there is a lower tendency to get snack drops from monsters you are actively questing for. (IE - You'll get fewer snacks from the trolls in Hammetsu village when you have to defeat them in one of those side quests than you will after you turn in the quest.
I've also noted that some monsters will drop more often than others. You may want to try a few different types and see which drop well for you.
You may also consider just continue leveling: the snacks are much better in Dragon Spire.