I noticed that there is an after-market 406 mount available on ebay, which looks to have a very similar bush (but the bracket is different).
I have asked the vendor to measure the diameter of the large bush, but he seems not to understand the question.
Does anyone feel like buying one on the offchance? (I have spent my budget for this year
[edit] The original source for these may well be: http://e-katalog.intercars.com.pl/?sear ... lnika.html