You can definitely catch Greens in central PA. Best bet is to find a smaller warm water stream or small impoundment. One good spot I always found for Greens was at the bottom of spillways of smaller impoundments that I knew had Greens in them. Redears and Bluespotts are pretty rare in PA though. The four common sunfishes in PA waters are Bluegill, Redbreast, Green, and Pumpkinseed. (Along with Rock Bass and both species of Crappie too).
In moving water Redbreast Sunfish tend to be the dominant sunfish in central PA, although Greens, Bluegills, and to a lesser degree Pumpkinseeds can be caught in streams too. Impoundments and ponds are usually populated by some combination of Bluegill/Greens/Pumpkinseeds. Redbreasts are rare outside of moving water.
Sunnies are my first love, even more so than trout, and I'm a bit of a nerd with trying to ID them. All four of the common ones in PA are capable of hybridizing with one another and the hybrids can get tough to ID...not unlike the wild/stocked/fingerling/holdover trout ID debate really. I agree with Tim above too...they can become real muts after a while with more than just two species in there. It's usually impossible to be 100% certain with hybrids, but you can make some educated guesses based on their characteristics. The top two are definitely pure Greens, but I agree on the third one being some type of hybrid...Green x Pumpkinseed would be my guess too. Pure Greens tend to have a finer spot pattern and less prevalent blue streaks through the cheek area. Their tails are usually very small and narrow as well. Pure Seeds don't usually have orange in their fins and their mouth is much smaller, more like a Bluegill. Looks like a mix of the two to me. I have caught some similar ones in areas where both are prevalent. In many small impoundments Greens and Pumkinseeds will share spawning beds where as Bluegill tend to be a little more selective, and will chase other non Bluegills out.
Greens are a blast though...I think they're by far the most aggressive of the common four, and put up the best fight for their size. They do tend to stunt out in terms of growth due to overpopulation, especially in ponds and lakes. Like FI above though, I've caught some 8-9 inchers in moving water.
