The OP is looking for 6D games. Last time I was at Rivers they only had 8D. The following have 6D for certain.
Philly Area:
Parx
Harrahs Chester
Sugar House
PA stores that DO NOT have 6D games (as of 3 months ago anyway): Rivers (Pgh), Presque Isle (Erie), Hollywood (Harrisburg).
Other PA stores: Not sure if they have 6D or not: Sands (Bethlehem), Mt. Airy & Mohegan Sun @ Mt. Pocono (Wilkes-Barre area), Meadows (Washington, PA).
If you decide to come to Philly area, PM for more details.