For help finding reports from the the First Battle of Bull Run or First Manassas in the Official Records of the War of the Rebellion
See Series I, Volume 2:
the index:
http://www.civilwarchest.com/official_records/S1-V02/1024/First_Battle_o...
http://www.civilwarchest.com/official_records/S1-V02/1025/First_Battle_o...
http://www.civilwarchest.com/official_records/S1-V02/1026/First_Battle_o...
Summary of Principal Events:
http://www.civilwarchest.com/official_records/S1-V02/300/First_Battle_Bu...