I think you already have the answer. Lucky the ones that can buy it. Here in Dominican Republic I still can find it. I problaby will have to order from internet.
Dear Fleabag,
I have this instruction from my website, it can be usefull to understand how it works.
The effect is just gorgeous, I couldn't make it shows up in the picture.
I ordered Mylar from Heirlooms by Sharon, a very nice lady and it is not as expensive as I thought (Psssst gave a link).
If you collected the butterfly alpha from my website, I'm glad to tell you that it also works with Mylar. I made one for my GD's cousin (5 years old) and she loves sparkling things. I think she will like this one too.
Hugs,
Yoriko
She has very reasonable prices
and a tutorial
and answers to all of your Q's.