Bureau de Change services also available in e.g. larger post offices, some department stores (Fexco counters) and hotels. Also American Express on Nassau St. and Thomas Cook on Grafton Street in Dublin. I don't know which if any are open tomorrow unfortunately -- could try ringing them in the morning.
Banks open on 28th, but that's probably not much use. If you are travelling, get it from a cash machine when you arrive. If you aren't travelling, would a credit transfer do -- do you really need cash?