All I can suggest is to start off with the details you already have, and follow them up further - e.g. search the parish registers that you found the baptism for Thomas, and work back to see if you can find a marriage for John and Catherine. Hopefully this will give more details on them - but be aware that some registers can be very basic.
If they moved to the parish from somewhere else, It could be difficult to work out where they came from originally, but probably the next step would be to check adjacent parishes.
As aghadowey just mentioned the correct spelling is Brockagh - and it's located just north of the town of Laragh.
Shane