I went to Michaels in the craft section and got plastic masks and just laid my gumpaste on top and cut out the eyes and the mask shape and smoothed on top of the mask. Then left on the mask to let dry. It is in my pics.
I don't know how big you need the mask to be, but you can look at my pics and I did a mardi gras mask cookie out of an upside down heart cookie cutter.
Also, if you have a Party City, they would definately have the masks so you could form a mask of of them.