Fish paper is available from Amazon or most electrical supply houses. Don't know how it got its name but the late, great Dale was always recommending its use.
From Wikipedia "Fish paper or fishpaper is a strong, flexible, fibrous dielectric paper. It resists moderate heat and mechanical injury, and is often used for wrapping coils and insulating stove-top parts. It is hygroscopic and so must be treated with paraffin for use in moist environments."
