Rim Fire,
I found serial # 2592 issued to the 6th Independent Company of Ohio Sharpshooters on August 16, 1863. All the 25xx serial #s went to the same unit. Actually both pages of Spencer Rifles from Volume 3 show the same Ohio unit, 5th, 6th, or 7th Companies as receiving the Spencer Rifles.
Hope this helps. What are you doing with all these serial # searches?