Agencies that typically (although not always) are part of the executive branch can have the authority to create rules and regulations.
Regulations are part of the larger category of administrative law, which also includes executive orders and administrative decisions.
The Pennsylvania Bulletin gets updated weekly and contains newly proposed regulations as well as revised regulations that were already made available for public comments.
This can be a good resource for finding new regulations or a collection of chronologically ordered regulations.
Unlike the Pennsylvania Bulletin, the Pennsylvania Code is organized by subject instead of chronology. This makes it easier to browse and locate regulations on a similar topic regardless of when they were created.
Westlaw searches the most recent version of the Pennsylvania Code and provides useful annotations that can direct you to relevant cases, law review articles, and more that discuss the regulation in question.