Posted 08 January 2012 - 10:05 PM
The Army Museums website have a file for 1912-1913 12L Journals. The ref is NAM Accession No 3265 and Class No BRITCAV 12L. Quite how you see them,or how much they want paid to look through them for you is another matter.
I once did a few War Diaries for an aquaintance,covering the first BEF deployments to France in 1914. One of them was the 12 Lancers,WO95/1140. In one or two of the Cavalry Diaries there were nominal lists of the composition of the various Squadrons,but I don't recall which ones as that wasn't my mission ! It might be worth a peek if all else fails.