I couldn't find this product online, but I found it at Wal-Mart. It is a box containing 800 stickers, in a cardboard box and sells for $5. It is produced by Paper Magic Group, Inc., based out of Moosic, PA. The same company also sold boxes of Spongebob Squarepants, Star Wars, and Scooby Doo, among others.
I've scanned the sheet of stickers which contain artwork based on George Perez's cover for AVENGERS #1 (Feb 1998) - they are Scarlet Witch, Hawkeye, and Quicksilver.