Everyone has always pointed to Bumper for a full sheet of mylar: http://www.bumper.com.au/products/parts/pinball-parts/mylar.html
Yepp.. I buy my mylar sheets from Bumper. They sell it in sizes large enough to cover a whole PF.. standard size and wide body size sheets. You always end up with some left over off cuts which come in handy for drop target faces etc, to protect artwork and so on.
I also use leftover mylar pieces to make cabinet protectors for under where the legs bolt on, to help protect a newly painted cab
