I have two additional sources for acetate in the USA:
Tara Materials Inc.
Lawrenceville, GA 30246
["Optically pure cast diacetate", 20"x12', .003 mil]
Bienfang - Hunt
Statesville, NC 28677
["Acetate, clear, No. 300AA", 40"x12', .003 mil]
Good luck,
Mark Wilson
Department of Geology
The College of Wooster
Wooster, OH 44691
mwilson@acs.wooster.edu