I did a quick search on the sizes, weights of frosted Mylar and came up with this site.,
www.posterprintersupply.com. It apparently available in a wide variety of sizes as well as in rolls. There are other sites out there but this will give you a quick idea of prices and sizes.
I don't know whether frosted and matte are the same, but this site refers to matte as used for drawing so I suspect it may be.
Thanks Bill for posting this along with your lovely example.