As Robert jnr was born c. 1840, he would have been too young to have had/rented land, therefore he wouldn't be listed in Griffiths. If his father was residing in Ireland, he should have been listed, unless he too was in the military?
I had a quick look on the IFHF site for a Robert Crawford born to a Robert Crawford in Kildare, but no records came up.
Do you happen to know Robert jnr's mother's name? Perhaps you could search for his parent's marriage, which would at least establish a place. Or do you know of any siblings of Robert's?
Sorry can't be of any further help.