I concur with Gordon as to the number of images you include and which ones you include. Your portfolio is a bit like a CV which should be customised for each job you are applying for. So, keep the number of images down and only select those which are relevant at any one particular time.
As to where to get a suitable folder, well, Northern Ireland isn't going to be much use to you (with apologies to those that suggested Calumet or WH Smith).
I suggest you take yourself along to O'Sullivan Graphics - if they can't help you out, I don't know who can. They used to be on Grantham St. (I think they still are) and now have a store on Camden St. I used to shop there regularly for all sorts of things when I lived in Dublin - portfolio folders, mounting board, foamcore, double-sided tape, flourescent paint, mount cutter, etc., etc.
Hope that helps.
- Thorsten.