I don't believe there is anywhere on WDW property that you can obtain the "advance purchase" rates.
However, you can buy through Disneyworld.com the night before you leave and select the "Will call" delivery option. Or, there are a number of REPUTABLE third-party vendors through whom you can buy official WDW passes. Among them are Ticketmania, Florida Orlando Tickets, Paramount, etc. Many of these vendors have offices right in Orlando where you can pick up your passes --often saving shipping costs and some even offer additional promotions for pick-ups. Some will even deliver your passes to the front desk of your resort.
The margin of savings from one vendor to the next is fairly slim.
I would suggest avoiding eBay or any roadside vendors that might try to sell you a pass. Other than that, there are many respectable alternatives to buying directly from Disney.