The Audubon Society of Western PA's Center for Native Plants is having its annual native plant sale this Saturday, May 3rd from 9am-2pm at the Beechwood Farms Nature Reserve. See here for details:
http://www.aswp.org/acnp.html I'm not affiliated with them, but I picked up some really great plants two years ago. If you love gardening, I'd highly suggest the sale.