I've never used mylar templates, I'll have to look into them. A quick search of mylar eep suppliers showed me Plainjanethreads.com (I have no affiliation, but it looks interesting!), also saw a few on Amazon, so there must be plenty of sites that sell what you're looking for. I've been using thicker cardstock paper for years, just run a piece through my printer and print a template from TexasFreckles.com's site (it's free to use) and cut it using an old rotary cutter and scissors. Good luck in your search!