I use acetate to smooth/polish fondant. I got a sheet of overhead projector film and cut it to size. You can also find it as the clear covering on some document folders, but I use the OHP film.
HTH
Any office supply stores, I use the acetate they use for projectors.
that is too funny !! 
I thought you meant as an additive. I couldnt figure out why you would want to add it.. but i like to experiment and thought "oh well." hubby uses the additive in his homebrew, that i how I found out quite by accident where to get all my additives.
are you talking about something like a mat? 
I buy my acetate sheets from JB Prince http://www.jbprince.com/pc_combined_results.asp?search_prod=(searchlike~p.nm~acetate|Or|searchlike~p.ds~acetate|Or|searchlike~p.sku~acetate|Or|searchlike~p.opt3~acetate|Or|searchlike~p.opt5~acetate)|and|&search_keyword=acetate&page=1
and Kopykake also sells acetate. If you cannot find it or cannot afford it, I've heard that freezer paper works well as a substitute.
I buy it by the roll at aaron brothers. Or you can use high quality page protecters.
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