Have you tried Equipet? They sell a lot of horse-related products, but I don't know if they sell those mats. They have branches in Navan, Ashbourne and Drogheda, but the only one listed in the Golden Pages is the Ashbourne branch, if you want to give them a ring. The number is: (01)8352702.
Oh, and a quick search on Google found this site: [broken link removed]