Talked to a couple different dealers today, including Ducati Omaha, whom I previously regarded as one of the best sources for parts, even for old bikes. Seems like Ducati has taken a new line (well, new to me) in regards to how far back in their history they're willing to support. In a nutshell, anything older than 1991 is s___ out of luck. Part numbers still cross-reference and may still be readily available, but apparently there is no more microfiche support for anything prior to '91, at least through a dealer.

I was kind of shocked.

The last bike whose there are the parts into Ducati spare parts web system is the 907.
So, you can ask for 907's parts (assuming you need for parts which fit both the bikes).
Ciao