You could try Manor Stone, based in Co. Laois (they're in the book), they do a lot of pebble/ shingle (plus building stone etc. and they do runs to Dublin (or they did last time I bought from them). I paid €90 two years ago for a 1 tonne dumpy bag, delivered to my door. You probably won't do much better in price, it's dear stuff but looks the biz, you can buy the regular grey (limestone) pea gravel for a fraction of this price but it's not as effective, especially in small areas.