For the first one, you can omit the article if you pluralize pharmacy and store-- this makes it very general and then allows the article to be omitted. '...can be sold through pharmacies or stores.' For the second, you will need the preposition 'for,' because the animal is searching 'for' something, in this case shelter. It can then include or omit the article with slight changes to the meaning: '...to search for shelter when the cold comes.' Here, 'shelter' is most general, i.e. just shelter against the cold, it doesn't infer anything more about the nature of the shelter. It's the general concept of 'shelter' as something that protects from the cold and the elements. '...to search for a shelter.' Here, 'shelter' would be less general, shelter would be a more specific type of thing (a structure, a building, a hole, a place, etc.) '...to search for the shelter.' Here, 'shelter' is most specific and is about a particular, specific shelter (the structure, the building, the hole, the place, etc.)

In your third sentence, you can use a different verb and then omit the article. Animals need to seek shelter. Animals need to find shelter.

You search a place for something. If you lose your keys, you search your home for your keys.

Hello! I'd be happy to help correct those sentences for you: "Chamomile tea is a remedy that can be sold through a pharmacy or store." "Usually, wild animals need to search for shelter when the cold comes." I made a few adjustments for clarity and grammatical correctness. If you have any more questions or if there's anything else I can help you with, feel free to ask!