This is taken from the Department of the Environment's website
www.environ.ie
Refunds of Motor Tax
IMPORTANT: Tax discs must be surrendered immediately as refunds are generally calculated from the first of the month following the surrender of the disc. A minimum of three unexpired whole calender months must be left on the disc when surrendered.
Applications for refunds of motor tax can be made to you local motor tax office, on Form RF120, in circumstances when,
The vehicle has been scrapped/destroyed or sent permanently out of the state,
The vehicle has been stolen and has not been recovered by the owner,
A vehicle in respect of which a tax disc has been taken out has not been used in a public place at any time since the issue of the disc,
The owner of the vehicle has ceased, because of illness, injury or other physical disability, to use the vehicle,
The owner of the vehicle has ceased, because of absence from the state for business or educational purposes, to use the vehicle,
The owner of the vehicle has ceased, because of service overseas with the Defence Forces, to use the vehicle.
I would imagine that you should ask the dismantlers for the tax disc from the car and proceed from there.