I searched for information on the fairing well nuts. Yes, Ducati still sells them, but they are commonly available for about 1/5th their price. I just wasn't sure of the size.

The best information I could locate here was this cryptic information from the Paso 750 forum, parts interchange post:
viewtopic.php?f=1&t=2152&p=15958&hilit=well+nut#p15958
"Well nuts: 1/4 S Metric USM #347103 Well Nut 6mm (.015-.111 grp) http://www.klsales.com
T telephone: (414) 521-3003. Their web site has a chart of all sizes available."

Good luck with that. The website is obtuse and when I found the nuts in their inventory, none were in stock. And the USM# 347103 led to some specs at Parker Hannifin but no sources for small lots of the nuts.
https://www.parker.com/literature/ISS5809.pdf

It's obvious they are M6 nuts. I determined from Parker Hannifin and direct measurement they are ~12.7mm (1/2 inch) diameter and ~16mm (0.63 inch) height or length (when new and uncompressed) with a 16mm head. I found a good deal on Amazon, BUT what I received today are 21mm long, even though the description indicated they were 16mm. The 20mm bolt will not reach unless you scrunch them. So, my only caution in buying them online is to have some confidence that the seller is shipping you ~16mm long, shorter better than longer, well nuts.

Anyway, there are gazillions of the correct well nut available on eBay and Amazon.

So, here's the bottom line:

Look for well nuts that are M6x1.00, 12.7mm round barrel, ~16mm long with a ~16mm head.

Here's a lifetime supply of what should be correct. Should be delivered tomorrow. (UPDATE: They are perfect!)
https://www.amazon.com/gp/product/B0040CZ3R4

Another good source to search for is GM 20130258 used for luggage roof racks. Identical specs. There is another GM part that has a larger head (flange) that should work as well.

In the UK I usually but them off eBay

And as you've found out they come in different lengths and threads.

Thank you for the link to Amazon!
When I bought the 907 back in 2001 the PO gave me a tip on retapping something more commonly available but at $17 you can't go wrong.

Much appreciated!