for the sides of a bible cake, and is it possible for it to be on buttercream?

You can paint gold lustre or pearl dust mixed with vanilla or vodka . You have to do a few coats, at least, though (see my can of pate in photos to see if that's the look you want, though I believe it is). I don't think it works well with BC, but it works well with RI if you want to write in gold.

Americolor has a gold color if it doesn't have to be shiney gold. If it does you could airbrush it gold.