An excellent blog article on Pennsylvania Militia here at History and Ancestry.
"Besides trying to understand the Pennsylvania militia system, there aren’t many subjects that make you want to bang your head against a hard surface repeatedly like trying to answer the question: Just what in the heck did the Pennsylvania militiaman wear? But it is a valid and important question, is it not? After all, for those of us with ancestors who served in the militia, it matters a great deal what they looked like and what they wore. It tells us a lot about the character of an individual, the way they presented themselves. And for those readers who, like me, want to portray accurately (or the next closest approximation of) their ancestors’ attire for living history or reenacting events, you don’t want to get it wrong. At the very least, you’d probably like to be able to point to some evidence.
Arms and Basic Equipment from 1777-1783:
This is a stubborn question and the answers aren’t apparent. You see, under the ordinances of the Militia Law, County Lieutenants were given orders to supply, with arms and equipment, up to two classes of militia between 200-600 men, depending on the size of the county) for their district. The Lieutenants were also to assign someone to the office of County Quartermaster..."
It is a great read, I encourage you to take a look...