Hummm, you are not really all that close to anything down there… Do you have a Satnav (road or bike type?)
I’d get in touch with Racing795 – Road and MTB crew based around bunclody which isn’t too far away from you, their XC race course is excellent and there is a lot of other stuff around Mt Leinster that they know of.
Other clubs in that neck of the woods (ish) are MBCC (cork), I know they have trails in the Galty mountains, which isn’t too far from you.
MBUL (limerick) – 99% sure they don’t go towards Tipp very often (more Lough Derg neck of the woods), but Robert on there has millions of trails on Garmin which might be of use.
Ballyhoura is great (some longer trails but chat on MBUL for linking together properly), not too far from you, N24 isn’t a bad road – easy enough to overtake on most of it, just hope that you don’t Miss daisy afraid to overtake some tractor and then another 10 cars behind – I think it’s probably your best bet though.
After that you are looking at trails off the N11 such as (in closeness/ease)
Carrick Mt (Glenealy town, mainly Enduro trails, but doable as an XC head), needs a guide though.
Glen of the Downs (Brill beginners/fun trails, and a couple of class xc runs), probably get away without a guide.
Ballinstoe – purpose built trails which are nice (well designed, good trailhead support there), 20 min drive from N11 though.
Ticknock – more purpose built trails (not so well designed and no trailhead support) –furthest away from you too (but loads of other trails and would be easier to get a guide from a club like MAD/EPIC/IMBRC).