I don't think it will matter too much which area you've put it in out of the two - its got more chance being seen in general anyway!.
I've only ever been to Northern Ireland over there, and found generally that its easy to find around Belfast, and much less common elsewhere, but can still be found. With the exception of one pump in the docks area at flogas the rest were on or next to forecourt sites, and supplied either by calor or flogas. Theres very little competition on price though (check http://www.filllpg.co.uk
to see what i mean)http://www.flogas.ie/autogas/
shows you a map of their outlets - it might be worthwhile phoning round a few near your intended area and asking them directly if they sell it, and get an idea of how much if they will tell you
The map on the calor site doesn't seem to work properly.http://www.alternativefuelcompany.co.uk/Autogas%20Stations%20in%20NI.html
< This list is horrorifically out of date (and despite the title has stations in ROI as well).
Its also worth noting that the ACME filler is used there if you aren't already aware, so an adaptor or filler change needs consideration, but could always be done later.