Events shouldn't be aggravating or stressful, they should be fun. I've been stalking the shops for sugar and milk and sometimes nothing even stocks at all for an hour, much less the needed ingredients.
I propose that during events that require shop ingredients, that shop will stock the ingredients at least every other restock, and in a high enough number that it doesn't end up being pay to win. Let the random event item be the one thing that's a bit difficult to come by, not all the ingredients though.