Gold is a very good material for leaf-type electroscope. It is very soft and light and conductive, while being non-corrosive. Other materials can be used but none seem quite as good.
Gold Leaf is applied by adhering it to enamel paint sign writing which has dried to the stage where it is tacky. Any excess which falls wide of the painted lettering is gently brushed away.
It depends on the price most likely. Since real gold is trading at about $930/oz right now you would expect to pay over $30 for a gram of real "gold leaf flake". However, there are sites that sell...