Actually all big chinese herb store have the mix. My suggestion is to visit a trustworthy store that you know the boss personally (or the mother, or the mother in law or any auntie that knows them). Why?, the mix is pretty standard but it matters on the quality of the materials. And yes, chinese drug store sometimes do cheat their customers.

Eu Yan Sang is not that bad, but pls bear in mind, they are more expensive than others.

My case is that, I just pick them up from a big chinese herb store from my hometown, if he dare cheat, all my aunties will go to his competitor store.