Bit of a toughie Bash as I went through this last year, but I managed to extend my UK insurance by a further 3 months with some careful negotiation in extending my Green card, told them was on temp assignment, before they declined to go any further.
I then approached couple of Swiss insurers who insured my RHD UK spec car with UK reg plate- and had no problems in doing this. Did it through Winterthur.
The one caveat was that I was only insured for Switzerland!!! and not able to drive out of the country on that insurance.
Now on Swiss plate and Swiss insurance
Hope this helps