There are some handicapped spaces in lot 1 which at Pete Rose Way and 3rd. It is an outdoor lot that is the closest to the stadium. They are limited so I would get their early. I usually get to the Bengals game at least a few hours before the game.
Here is the info from the Bengals website about the parking as well as a parking map:
Every lot provides handicapped parking spaces for season ticket holders with passes for the lot. In addition, single-game parking is available for handicapped patrons in Lot 1, which is located at the corner of Pete Rose Way and Central Avenue.
Handicapped parking in Lot 1 is available on a first-come, first-served basis.