Embarassingly, even though I live right around from the Military Archives and I'm completing a research degree on Irish history I only recently went to the Military Archives and I can't believe I hadn't gone earlier.
They have an amazing collection there called the Burea of Military History. Starting in 1947, they interviewed and recorded the experiences of over 1773 volunteers from the War of Independence. They have an exhaustive list of these witness statements relating to all areas of Ireland and the UK.
If that's not it they also have tons of other information on the Free State Army and the Army during the Military. It's a small archive so you get one on one attention, which is amazing in an archive with so much information. The one downside though of its small size is that it's quite difficult to get an appointment, so you should definitely ring a month or two in advance of when you're hoping to attend. read more