Can't help with name of sites, though my vet recommended that I give my dog cod liver oil capsules, garlic capsules and sea kelp. Cod liver for joints, garlic and sea kelp for healthy coat.
VetMedic are very good online suppliers, and they have free Veterinary advice to offer so you can find the right treatment. Good for worming stuff & flea products too.
If your dog is suffering from disease then I would suggest you to do CBD treatment because it gives instant recovery from diseases. As you are looking for the website from where you can take medicine and joint oil for your dog then you can just take a look at https://www.cannacanine.ca/store. Here you can get all the medicines and oil which is related to the CBD treatment. I also purchased CBD oil for my dog from this website. They provide me the best quality of oil with some useful instructions to use it at an affordable price.