There is a place in monkstown called the audio clinic.I got my video camera repaired there a few years ago.He also had radios there too.He might be able to help you.They're listed in the golden pages.
Contact Tannoy or authorised dealers, they should be able to point you in the direction of someone who can swap out the speaker affected. you'll need the speaker to be an exact match of what was there to maintain the sound quality of the system.
Leo