We were just at Shady Maple market in the Lancaster, PA, area and they have packer cut briskets. I've seen them there before, so they must have them regularly. I bought a 13 pound one which I will cook for Thursday dinner. I also saw a 15 pound one, but didn't ask what else they might have had in the cooler.
Shady Maple is in the Blue Ball/East Earl area about 7 miles East of Ephrata. It's also a great place to buy bulk foods including spices.
More info at: http://www.shady-maple.com/
They also have a great buffet restaurant on the property.