Maybe someone else is aware of some single, comprehensive archive where all PCL codes "live", but, aside from finding a PCL Code Programmers Manual somewhere, your best bet has always been to go directly to the web site of the specific printer manufacturer and see what they have under Support or email them for information.
Good Luck,
JRB-Bldr
VisionQuest Consulting
Business Analyst & CIO Consulting Services
CIOServices@yahoo.com