Which wholesalers you go with depends on how you plan to structure your e-commerce business:
If you have the capital needed to stock inventory:
The first way to source products is to go directly to the manufacturer. By cutting out any wholesalers in the middle, you'll have far higher margins. But you'll likely need to stock more inventory as manufacturers often deal with larger order sizes. This can be risky if you don't know which products will sell (i.e. you end up buying 1000 quantity of a product and don't end up selling all of them).
The next (and most common) way is wholesalers. There are tons of directories and marketplaces to connect with wholesalers. They'll often require that you open up an account with them.
Here are some directories and marketplaces to connect with wholesalers:
If you don't want to stock inventory:
This is known as "drop shipping" -- where you first get orders from customers on your site and then place an order with the wholesaler and provide the customers' shipping address. The wholesaler then ships the products directly to the customer.
Drop shipping removes the complexity and the need to stock inventory yourself (which you might not end up selling). The downside is that margins are lower (as the wholesaler is doing the heavy lifting).
Some drop shipping marketplaces: