David, likewise I cannot trace any information indicating when a beast like this might last have turned a wheel.
With the GSR building new brake vans in the 1940s, I suspect that few if any were about by 1950 but I agree it would make a very nice thing on a layout. If it did last, it is very possible that instead of being spick and span, it might me more likely to be in a very tatty condition, with a barely discernible, badly faded "G" and "S" on its side!
There were six of these, and they were initially intended specifically for branch lines, particularly for Killala, Achill, Clifden and probably Loughrea and Ballinrobe. Following the closure of the first three of those, I would strongly suspect that they were done away with after the Achill line closed in 1937 - possibly earlier, as photos of trains on the Achill line show passenger brake vans in use more often, especially in later days.
They were, of course, probably black when built, as that's what the Midland did with wagons in the 1890s, but by 1918 anyway they were a very dark grey, lightening slightly to a more usual "wagon grey" (similar to LMS wagons in Britain) after the GSR took over. Obviously, a big "G S" on the side, and "M" added to the number, thus No. 52 becomes 52M.