The mica you would want is called Muscovite a pale almost colorless
mica. Comes in sheets called bibles or books. Because of the near
perfect basal cleavage is it possible to split off thin flexible
sheets. It is what the old timers called isinglass The heatproof
windows in old time stoves and ranges. The reason it pops apart when
heated is you are driving off the water contained in it. About 5 per
cent is changed to steam when heated. This being a silicate mineral.
The infamous vermiculites that have caused concern because they
contain asbestos dust are mica minerals that are heated to a high
temperature to caused expansion to form a light material used as
insulation and planting material.
The best place is you can’t locate old electrical appliances to take
apart is enamel/potters suppliers. Also for smaller sized pieces
this surplus electronic sight has them for sale.
have purchased them and they are what they describe. this place has
some great pricing on things electronic. Long time customer