I would guess you would get them in Tullys over beside Smyths toys…. I got bra extenders over there when I was pregnant.
Good luck, I know what your loooking for but never seen them on sale
I got something similar called strap trap from this link http://www.breasttalk.co.uk. You get loads in a pack just stitch them into the shoulder strap of your clothes and you can catch your bra strap onto it. They stay in your clothes can be put through washing machine.
As far as I remember took about a week for delivery.
i sell bra extenders pack of 3 white /black/nude for 7.75 .
i work for ann summers and i live in meadow view drogheda . so i have some here if you wish pet.
or if anyone would like a party or book just shout me .