Definitely work through everything you can in the Scottish records first. If Samuel and Hannah had children in Scotland then they probably died in Scotland too? Scottish death records are very good and you might get a mother's maiden name from one of those which is more than you could hope to get from most Irish sources even if they exist and you can find them.
If they moved to Scotland in the 1830s-1850s then there would be a very strong chance that they had siblings or other close relatives also move to Scotland. The scale of emigration at that time is staggering.
Carefully look at anybody living at the same address on a census record or at marriage witnesses, etc. The more relatives you can find from Ireland, the better chance you have of figuring out where they came from. You got really lucky even getting the counties on that record! I haven't seen that on any of my Scottish civil registrations.
