That's a pretty big haystack. About 272,599 Model 1842's were fabricated between 1844 and 1855 at the two national armories.
At least 65,000 muskets made as percussion (i.e., model 1842's) were delivered to Federal arsenals in the South in 1860 on the orders of Secretary Floyd. Those largely became available to Southern forces in early 1861 as various states seceded and took over federal arsenals within their borders. Other smaller numbers of M. 1842's were already stored in some of those arsenals and additional muskets had been delivered to various southern states as part of their annual allotments under the Militia Act of 1808 (while the Ordnance Bureau preferred to deliver contractor-made Model 1816's (either in flint or altered to percussion) under the Act, some states insisted on and received the "latest, improved muskets" (i.e., model 1842's).
The Model 1842 was a significant Confederate arm as well as Northern, particularly during the first half of the war. So you have a large number of regiments to look at.