The C class was bought for branch use, and closures reduced the need for them, so a lot were out of use by the end of the 60's. A branch surviving would probably have had one in preference to a 141, which would have been out on main line work. A railcar set was used on Thurles - Clonmel. 60's carriages GSW or GSR or early CIE built, with 70's early-CIE. Alas, most of these are not RTR - yet!
However, what RTR is available would not be much hardship while you wait. God bless all the manufacturers, who continue to amaze with the gaps they are filling.