You aren't going to find many of these brands for 'wholesale' because they often only sell directly to specific retailers. For instance, Coach won't let just anyone carry their products.
There are products that you are going to have a hard time finding 'wholesale' pricing for unless you buy TONS. If D&G sat around selling individual jeans for wholesale prices, there would be no market for D&G in retail stores.
So I guess the answer to your question, in my opinion, is that you are probably out of luck aside from eBay individual items.