XBOX One Controller battery cover - where to find replacements?

Hi there!

I have 2 XBOX controllers, one with a damaged cover that keep falling off and one with none. I was looking for a way to find a replacement but can’t find any good and cheap sites.

Does anyone know of a good site, and what to specifically look for? These are the standard XBOX one controllers with BT and removeable AA batteries.

Also, looking for thumbstick covers.