I have now taken delivery of a batch of 16" city jets (rear tyres for the c5).
It has taken some effort but we got there in the end...
Not sure how many more of these I will be able to get so if you need some my advice would be don't hang about for the next lot !
I'm still trying to source some alternatives, finally found one I liked to find that it was also had to source
C'est la vie !