Kieran,
You'll need to register here to get full details. Not automated, but worth the wait.
http://www.ontrackplant.com/sightings-of/ireland or http://www.ontrackplant.com/sightings-of/northern-ireland
Not many are 00, the bachmann tamper in particular looking well below even H0 scale to be fair. More like 1:100 almost compared with a 1:76 model.
The brittania pacific model is really very close to the Irish prototype, but the roof needs some revision, along with the addition of pneumatic hoses etc, a job you'd tackle with ease. It's the best resin casting I've ever come across, really is top of the line production. If I can dig out photos of the one I irish-ised, I'll post them later.
http://www.dckits-devideos.co.uk/shop/track_machines_tampers_overhead_catenery_infrastructure/clockwork_ideas_and_tamping_machines/plasser_08_16_c80rt_c100_rt_tamping_machine.php
The other ones available are the Veissman tamper - really looks superb, closest to an Irish vehicle is 742 (don't hold me to that, I'll check later.
742 at Kildare PW, 4/4/15 by Kieran Marshall, on Flickr
Lastly, if some of the younger members on here want to see what and early "Netscape" type website from about 20 years ago looks like, its Linea Models in Italy.
http://www.lineamodel.it/benvenuti_in_lineamodel.htm
the kits are top of the range H0, but pricey. the APT model is is €500. They have other per way stuff, but that site is giving me a headache.
HTH.
R.