I had a good experience recently with sellitstore...
http://www.sellitstore.com/mylar.htm
You can even request a free one by sending them a SASE.
After sending this site an email re: their mylar holders, I received 5(Five) free samples, which included three different sizes. Assuming they are mylar as advertised, they seem to be just as good as any other mylar holders that I have purchased in the past.
I would suggest giving them a try before assuming the worse.
And by the way, I didn't even have to supply a SASE. They paid for the shipping.
And what was really neat.....The front and back of the envelope had 29, that's right twenty nine postage stamps. And all of the ones on the back weren't even cancelled.
FRIEDSQUID