Beachbuggy can get OEM rings. I ended up paying £80 for some Nippon ones from eBay.
There's loads of info in my thread if your doing an engine build as I rebuilt mine 3 weeks ago.
I got mine from Jason at All German Parts.
Proper Mahle items too.
superb pricelooking back at my invoice, it was £17 per ring set +vat, so £82 for a set of four all in.