PA has a prep class that s offered. I have seen it in Delaware county, but im not sure where else. This is our local chapter of the ISA web site. They do an ok job of keeping up with it. http://www.penndelisa.org/
I would say your best bet would be to study study study and take the exam at the Shade Tree Symposium in January or february. They always offer the tests the sunday before the symposium.
I hope this helps. If you have any questions let me know Im from PA as well, South east corner, but pa none the less. Where abouts are you from?