Greetings, 1776. How appropriate (for us Americans) that you'd post up on the 4th of July. July 4, 1776 is the day the US declared independence from Great Britain.
Anyway.....I'm pretty sure all of the license plate holder parts are still available from Ducati except for the "x-bracket" that bolts to the muffler assembly and holds the rest of the parts. However, David Purcell, a list member in Salt Lake City, Utah, USA makes a machined version of that part that looks every bit as good as the original. You can find reference to David, including contact information, in another thread on this forum. Just search for "x-bracket". I know this because mine disappeared on a cross country trip....but that's another story.
The tool kit should, likewise, be available from Ducati, complete with Owner's Manual.
The exhaust might be a problem. Keep posting here and look out on ebay until you find one. Several owners use aftermarket exhausts, but keep the originals for the sake of sellability. However, an MH is occasionally wadded (blasphemy!), so you might eventually find one being salvaged if you're patient.
Good luck, and keep us posted.
'02 MH900e #1501
'95 900 SS/SP
'67 Aermacchi/HD Sprint SS 250/CRTT wannabe