Paul,
You need a pair of DUB 100640MMM.
Damen & Kroes in the Netherlands still has stocks. I don't know the price they're asking but they don't do discounts. The original retail price was £70 a pair.
Here's a hot tip for you. If your rear silencer is no longer OEM, the tailpipes may not be aligned accurately so the extenders may look slightly wonky.
Simon