Businesses buy wholesale printing paper from wholesale suppliers, which they can find by contacting manufacturers for lists of their authorized wholesalers. They can buy wholesale once they have federal employer IDs as well as state tax IDs since they need to withhold the taxes on their sales.
There can be other opportunities to buy wholesale printing paper. Sometimes, a business can buy right from the manufacturer rather than its authorized wholesalers. Other times, businesses can buy overstock, which is excess inventory that is sold off at discounted prices. However, businesses need to scrutinize such opportunities to make sure that they are genuine rather than scams.