There's an Irish group on Ravelry
by the way. Where do you live? I have a map of all wool shops in Ireland I made here
, some have a better selection than others!
I have used Sirdar Denim Ultra in the past, which is only 10mm needles not 15mm, but it depends on the pattern and whether you would need to modify it a lot or not.
Rowan big wool is nearly the same recommended needle size, but is prob more expensive