The area around Boiling Springs (Allenberry Resort) is easily accessible as are the waters around Falling Springs. West of Boiling Springs, toward Mt. St. Holly, the Breeches is smaller but there is ample places to fish. Check with Yellow Breeches Outfitters (online) for more information (see link below). For Falling Springs, contact Mike Heck (FallingSprings.com) or for South Central Pa, check the weblink.
Yellow Breeches Outfitters
Mike Heck Trout Guide
Central PA Fly Fishing - Fly Fishing info for Central PA Trout Streams