Thanks for all the replies to my question about sources for 'fat tubulars'.
I was able to find a web site for Dugast, that appears to provide an on-line sales facility:
A nice site that shows an intention to build the business through direct contact with cycling enthusiasts.
I have placed an order, which in effect is like sending an email to them requesting the required items. I received a reply saying that they would follow up with me to confirm and complete the transaction but have not heard anything after a couple of days. I'll report back...
Girton, Cambs., UK.