Once you know the distributor, you can contact them to see if they are willing to sell to you, and what conditions apply. Sometimes they will, sometimes they won’t and sometimes they will refer you to another distributor further down the food chain who may be more suited to deal with you, depending on your size.
It really is as simple as that, if you want to set up a real online business venture. Once you know a distributor, they will also be able to provide you with other products or know of other distributors who can help you.