Jimmy – You could try contacting the Irish Traditional Music Archive, whose website is www.itma.ie    I couldn't get the big bad blue clickifier to work, so if the link fails, just type in the URL www.itma.ie

The curator who runs the Archive is very knowledgeable about resources that touch on anything with trad music content, and if he doesn't know, he may be able to put you onto someone who does. There's bound to be a copy floating around Dublin SOMEwhere.

O'Riada was also connected with University College Cork, so someone in their music department library may be able to help you (Music Department, UCC, Sunday's Well Road, Cork, Ireland).

Here's some bumf from ITMA's website:

WAYS TO MAKE CONTACT WITH THE ARCHIVE
To make contact with the Irish Traditional Music Archive, you can
•        Visit the Archive at its premises at 63 Merrion Square, Dublin 2, from 10-1 pm and 2-5 pm, Monday to Friday inclusive, throughout the year. We are closed only on Irish bank holidays and from Christmas Eve to New Year's Day inclusive.
A visit is naturally the best option for benefiting from our collections and information resources. An appointment is not necessary, but if you have special requirements or wish to talk to a particular member of staff it is advisable to phone before travelling.
•        Write to the Archive at 63 Merrion Square, Dublin 2. We try to answer brief reasonable questions if we can, but like every other library or archive we do not have the resources to read books for you or do your research for you.   
•        Fax the Archive at +353-1-6624585.
•        Phone the Archive at +353-1-6619699. Again we will try to answer brief reasonable questions if we can.
•        E-mail the Archive at info@itma.ie