If I looked at the right design..."embroidered mirror covers"....I'm assuming your design is like free standing lace.
I hate the clear plastic like stabilizer. It always tears while stitching.
There are 2 mesh type stabilizers, that wash away, that I know of & have used.....
OESD Aquamesh several sizes:
http://www.sewingpartsonline.com/emb...bat:Stabilizer
Vilene WSS several sizes:
http://www.worldweidner.com/Vilene-W...izer-60in.aspx
Both come in different sizes. They aren't cheap, but if you figure right you can get a lot of designs out of each roll, without too much waste. A tip: Use left over pieces & a tiny dot of water, or lick your finger & press the pieces together. Let dry & hoop.
Where to buy it.....there are many sites that sell both. The price would depend on the size you need, your location, shipping costs, etc. I posted 2 sites that sell it. You may find a better price if you search.