There is a web site that lists alternative items that can be used for some of the older Dukes:
Ducati Parts Interchangeability List It listed a Mini 850 starter solonoid as being a suitable replacement for my 92/93 900ss.
Sadly, when I went to my local auto-electrical dealer they said the item was no longer available, however - they offered a replacement that works a treat.
The main name on the box is DURITE and the main part number appears to be 0-335-01, the rest of the text being:
Solonoid starter, Replaces 76771, 12Volt
Then the number 182308 which might be a local store code for the shop.
It cost the princely sum of £8.50.
Sadly, there is quite a bit of rewiring and changing connectors to do but its all pretty straight forward - and if an electrical dunce like me can do it - anyone can.
the only real problem that I found after some considerable time is that the solonoid frame actually needs a seperate earth.
The new unit is slightly bigger than the old but is zinc plated so hopefully will last longer. I even managed to mount it in the same position by robbing one of the old mounting lugs. Some knuckle scrapping late and it fits a treat.
My big red dog starts on the button every time now
Good Luck - Frank