Wow $0.90/gallon cheaper! Around here it seems to be $0.30- $.40/cheaper per gallon.
And around here in SC (nope cant help you on the Pa question just reading) regular gas stations do sell off road deisel, if they have a market for it. The two places i get it are in small towns but bigger than the one i live in which has nothing, literally nothing. These stations sell it to landscapers with deisel mowers road mowing crews for the city farmers, tractor owners and loggers.
We are in an area where logging is huge, find where those guys buy theres as they tend to buy a couple hundred gallons of it every other day, not all get it delivered. There is usually a station in every farming town or logging town where the guys fill up there transfer tanks or their fuel trailers.
But unlike Lbrown said i go to the regular gas station and buy offroad from the pump. In Greenwood, SC there is a regular BP which sells offraod from a pump right next to Onroad. We must be different here in the south than other areas.