15 inch by 20 inch acetate sheets

["Sheilah T. Broughton 904-294-1701" <BROUGHS@MAIL.FIRN.EDU>]

Does anyone know of a source where I can purchase clear acetate sheets that
are 15 inches by 20 inches.  Our school needs these for teachers to use as
an overlay on Big Books so that they may circles certain letters or
emphasize certain words.  A roll of acetate will not work as they need to
be able to pick up the sheet and move it from one page to the next.  The
acetate sheet must be stiff enough to stand up when leaned against the page
of the books.  Thanks for all your help. Please e-mail me directly at:
brought@mail.firn.edu