there's an shop run by a cranky old man that almost exclusively sells second-hand hubcaps, he almost has any make imaginable. It's on N11 at loughlinstown, just after cherrywood exit and before the Shankill roundabout that leads to M50/N11 merge.
I bought one for my previous car (volvo v40) there for around 12 or 15 euros a couple of years ago.