Dellorto SS1 spares

I have a ‘56 Airone and the throttle slide looks quite worn. I have done an online search with the usual suspects but nobody appears to stock them. Frustratingly, they tend do display them along with all of the other parts, but when I click on the image I am told that this item is no longer available.

Can anybody advise me where I can find a new, or good secondhand, throttle slide ?