If you live in Allegheny County: http://www.sheriffalleghenycounty.com/firearms.html
If you live in Washington County: http://www.co.washington.pa.us/Faq.aspx?QID=143
You will need:
Identification – (A CURRENT Pennsylvania Drivers License OR a CURRENT Pennsylvania Identification Card)
NOTE: The primary and secondary identification MUST have the same address on both.
Two References – ( MUST include FULL Name, FULL Address & Phone Number; CANNOT be family member and MUST live in Pennsylvania.)