Buying things wholesale can be done anywhere, including from the vendor themselves.
That isn't your question, you want to know how people get large lots of product at cheap cost, especially new items. New items usually come from a store warehouse that has discontinued the item and is liquidating their stock. USED items usually come from businesses that have upgrade or gone out of business. Businesses can opt to try and sell it themselves on ebay, but MOST of the time it is handled by liquidators who specialize in selling lots of hardware fast using a number of auction sites and online message boards like craigs list. These are the guys you see selling used hardware cheap as "untested".
What you see on ebay with people selling them cheap one by one is individuals or small companies who specialize in buying cheap lots of items that they know will make money by re-selling individually.
The chance of your friend finding what he needs in the liquidation auctions are slim and none, its always a case of being in the right place at the right time. however he might run into a re seller who will sell him the lots that they bought +profit. Just have him contact ebay sellers who are selling en-mass using buy it now.