Are you looking at a certain bike specifically or just wanting a Bianchi in general?
Old catalogs are available online but sparse. Users T-Mar and Bianchigirll have extensive knowledge and catalogs at their personal disposal. If you find a bike post detailed pictures and the forum can help.
The Bianchi Celeste color has changed over time. There is not one "Celeste".
Regarding decals, for a big brand like Bianchi there are a lot of repros made, but a more obscure decal might require you to get it custom made from a photo, which is expensive.
I would stay away from repainting unless absolutely necessary.