I have an old letter and the address is Clooncun, Clonberne, Ballinasloe
My Dad (now passed) and his brother visited sometime in the 1950’s and remember staying in a house that used to be an old pig sty (lovely!) and it had bullet holes in the wall. The also used a pony and trap. I believe the Mitchells sold Turf from that area. They also had possible cousins called SLATTERY and think o ne of the Mitchell sisters married Slattery.
The names Una and Marcelle also crop up a bit as to a Matitza? Mitchell.
You could have a look at the more recent death records for that area on http://www.irishgenealogy.ie. They go up to 1965. Ballinsloe would be the relevant registration district. There’s 12 Mitchell deaths in that SRD between 1950 and 1965. Marriages on the same site also go up to 1940. You can use the commercial sites to search indexes only for marriages up to 1958.