Andor's Trail

I looked through the topics here and I can't find any reference here to the Brimhaven quest "A Cat and Mouse Game" other than

"Give Seviron rocks, cheese and a bottle from Arlish".

Is Arlish supposed to have these items in the store? I can't find any rocks anywhere, including in the store with Arlish, to give to Seviron. I have searched everywhere possible for the rocks to no avail. Am I missing something? The store with Arlish only has a few items, some weapons, clothes, and a bottle of milk, not any empty bottles or rocks. I can get the cheese no problem, but where do I find the rocks? I go to Arlish after initiating the quest with Seviron and nothing has changed in her inventory and the dialogue is still the same as before the quest. Is there something that I need to do to make it so that she has the items for this quest? The quest list for "A Cat and Mouse Game" only says:

Seviron: Thanks. Just bring me the items. I think three rocks should be enough.
(You): I have the rocks and the cheese.

But this doesn't tell where you get the rocks at either, and as far as I remember, there's no store with rocks in the inventory.

You have to give the rocks and cheese before you can get the bottle from Arlish. Rocks are not sold, but are dropped by several monsters. Gargoyle cave is the easiest source.