"Committee of Safety Musket" is probably one of the most overused and misunderstood terms in American arms collecting. Tom Patton is entirely right in saying they are extremely rare. There might be less than a dozen real ones although there are probably thousands of muskets assembled from parts to which the term is applied. Even granting the term a very broad definition and including the majority of assembled muskets whether they were purchased by a Committee of Safety or not, there aren't many of them. My own opinion, based on my 40 years or so of studying New England arms, is that the majority of assembled muskets date from the first 25 years after the Revolution.
I remember two friends of mine discussing this at a gun show once. (Both of whom are as knowledgeable as anyone in the area of early American flintlocks) Friend #1 says "How do you tell if its Revolutionary? Friend #2 replies "Thats easy, if it belongs to you its Revolutionary. If you're trying to buy it, it isn't."
That said, I know that the Pennsylvania Historic or Museum Commission (I'm not sure of the proper name) has one because the gentleman who gave it to them was a friend of mine. Its very similar to a Land Pattern musket, I think with a 46" barrel though its been many years since I've seen it. The real Committee of Safety muskets were rare when they were new and probably shouldn't even be considered "typical" of what a volunteer from Pennsylvania would have carried.