That Pet Place just outside Lancaster is my best (and only) suggestion for Harrisburg area. I live in Western PA now, but I lived in Lebanon County for three years, and TPP was very good. I'm not sure where you've seen mixed reviews of it, but I've never seen anything really bad about it here on TPT. You probably won't find rare plants, but you'll certainly find anything common there.
But I'll also point out that you would pay less and find a larger selection going with an online retailer. I used aquariumplants.com and was very happy with it.