I brought my son Charlies christening shoes in Guineys in North Earl St and got the hat in tommys in Northside their the only places in Dublin to sell without buying the outfit
I got my christening shoes for Ella in Roches. I know they are no longer Roches and are now Debhnams but I am sure you would get some in there. Have you tried the little shop in the town between the Bracken Court and the Chinese. They have loads of kids clothes in the window and I would not be suprised if they did some shoes.
I know it's a bit far out, but I got the cutest pair in House of Fraser in the Dundrum shopping centre and they weren't that expensive either. They look white in the picture but they were actually ivory. The photo doesn't really do them justice! They were like a little pair of boot runners with ribbon instead of laces.