I just bought a Celeste Bianchi and it came with a pack of spray paint - one can Celeste and one of clear. I think it must have come from the Bianchi store since it's 'official' Bianchi paint and all the writing is in Italian with English as a second language.

You might try a bike shop that sells Bianchi to see if they can get it, otherwise try a pro auto paint store. They can match your paint, mix up a 2-part finish and put it in an aerosol can. Just make sure you understand how toxic 2-part paint is if you go that route.