In Ireland - it is hard to find many clothes shops that cater for teenagers or men under 30. Most mens clothes shops stock the same type of stuff with the same makes wherever you go.
If you are looking for anything different - you probably have to travel a bit to find a shop that might have what you want. Even then - they can only stock so much stuff - so they might not have what you want. Shopping online for skate and surf wear is much easier - but do they deliver to Ireland? Well here are some that do.

Blackleaf Clothing sell clothes from well known labels in the surf and skate world - such as Vans, Ripcurl, Nixon. Delivery to Ireland is available and charges depend on weight.
Extreme Pie -also sell a wide range of surf and skate-board wear. T Shirts , trousers, hoodies, shoes, sweatshirts etc. Brands such as Bench, Quiksilver, Roxy, Fox, Vans, Animal, Reef, Ripcurl, O'Neill, Nixon, Etnies and many more. Delivery to Ireland for up to 30kgs is a reasonable £10.00. GBP
Route One sell clothing aimed at bmx and skaters. Brands such as Berny's, Billabong, Birdhouse, Blind, Blueprint, Bones, Bootleg, Bravado, Carhartt, Chocolate, Circa, Cliche, Converse , Destructo, Diamond, Stussy and many more. They also sell skateboards and shoes. They charge £16.75 per order for delivering to Ireland. Seems high - but if you buy a lot of stuff it works out OK. (Petrol or a train ticket to Dublin could cost you more!)