You're not finding much info because there simply aren't that many off limit places. You see, in PA, the Right of the People To Keep and Bear Arms For the Defense of Themselves and Their State Shall Not Be Questioned.
Here's the short list:
-Courtrooms and judge's chambers...by law they must offer secure storage at the door. Some courthouses scoff at this law.
-Casinos
-K-12 schools*
-State parks**
The Allegheny county airport thing is not consistent with state pre-emption, which prohibits political subdivisions from having any say on issues of posession. I don't know what, if anything, the courts have said on that.
* There is a lawful purposes exemption language in the statute that has not been well tested in court. As they say, the possibility of prosecution exists.
** Again, an ambiguity and conflict in the law exists that has not been clarified in court. The practical standing is that if you are discovered to be armed in a state park, you will be asked to leave. If you do not do so immediately, you will be charged with criminal trespass.