I have listed a number of 750 Breva parts on ebay, bike now gone (still have a Falcone, Stornello, Lodola though) these were spares
All were off a running bike and will save you a fortune to buy or even more to fault find before you then have to buy
I have ECU, ignition switch complete with 2 keys, relay loom with relays etc etc
Search ‘Guzzi 750 Breva small bore’ have a look
Always open to a haggle for a job lot