I just looked up the Koss site, found the correct pads, and made an order using a credit card.
Here is a direct link to the Koss Pro4AA replacement pads. The set of 2 cost $5.46 (including sales tax) with free shipping via United States Postal Service. The order came directly from Koss in Milwaukee, Wisconsin, and it arrived at my home in Tennessee in 5 days.
Includes two PRO4AA replacement ear cushions and screen/foam assembly.
koss.com
Here is my instsllation experience and advice. Look at the bottom of the thread.
Koss Pro $AA Pad/Cushion Replacement