Unfortunately, there is no
Irish keymap in the "kbd" Linux package.
What you could do is create one yourself modify the uk one, that is /usr/share/kbd/keymaps/i386/qwerty/uk.map.gz.
Copy it somewhere, run "gunzip uk.map.gz". That command will output an uncompressed file uk.map that you can edit, as it's actually just a text file. When you are done, rename it "mv uk.map ie.map", gzip it like this: "gzip ie.map" and put it in its place as root: "cp ie.map.gz /usr/share/kbd/keymaps/i386/qwerty/".
You will find guidance to edit the map typing "man keymaps".
For the X keyboard the situation is better. Here are the available settings:
X Keyboard Layout: ie
X keyboard Variant: none needed[1]
[1]Available X keyboard Variants according to /usr/share/X11/xkb/rules/evdev.lst:
CloGaelach ie: CloGaelach
UnicodeExpert ie: Irish (UnicodeExpert)
ogam ie: Ogham
ogam_is434 ie: Ogham (IS434)
As a bitmap font you can use terminus, ter-1* (covered codepage ISO8859-15 for new orthography)[2])
True Type Font: DejaVu Sans Mono (include the 80 glyphs needed)
[2]Old orthography needs ISO8859-14 because of these glyphs:
Ḃ, ḃ, Ċ, ċ, Ḋ, ḋ, Ḟ, ḟ, Ġ, ġ, Ṁ, ṁ, Ṡ, ṡ, Ṫ, ṫ
according to this page:
http://en.wikipedia.org/wiki/ISO/IEC_8859-1
but can't you use the proposed workaround?