Having had some problems with leaking fuel tap (that would be the Manual one not the Vacuum tap) I have been looking for a new one for a long time, but have found them impossible to get! I was aware that the Cagiva 350/650 (black finish) and the F1 (clear finish) taps are otherwise identical despite having different Part Nos. I found some (Cagiva) black taps on e-bay with an Italian seller at very reasonable prices and have bought a couple, which I have just received. They are in original packing and brand new. I am not sure how to post a link to e-bay but they are eBay item number:223496703376. They also show up on UK e-bay if you search Cagiva fuel tap. I have just looked and the seller has only 5 left, so you would need to be quick!
If you are successful and prefer clear finish, the black rubberised coating comes off quite easily with paint stripper (I used Nitromors) any stubborn bits can be removed with toothpicks without marking the alloy. Best to remove the plastic on/off ring to do this - lever (5mm bar) is a press fit and can be knocked out with a pin-punch