I wasn't aware that any Medium Cs were sent to Ireland (at least not from memory). Medium Bs certainly were and also Mark V*. I think I've recently seen a picture of a Mark V in Dublin, but I need to check that.
"When the 17th Armoured Car Battalion arrived in Dublin in January, 1919, two of its three companies were armed with tanks: Company 'A' = 14 x Austin armoured cars, Company 'B' = 16 x Medium A 'Whippet' tanks (not to be confused with the Rolls Royce armored cars that, having served with the British, were nicknamed 'Whippets' by the Irish to whom they were handed over in 1922), Company 'C' = an unspecified number of Mark IV tanks, later replaced by Mark V* and Medium B tanks."
I thought it seemed a bit odd that they'd use Mark IV and Mark V* but not the more maneuverable Mark V, so your Mark V in Dublin is interesting.
This is just a quick response as I need to do some delving to check out my thoughts about a Mark V in Ireland. However I'm much clearer about Mark IVs. The 17th Battalion arrived in Ireland in 1919, but they didn't bring the Mark IVs with them. These were already there, having been brought across by a Special Service Company of N Battalion (later 14th Battalion) in 1917.