I found this Microscope Image Guessing Game on the TeachersPayTeachers website. The game has a variety of images of different pictures from under a Scanning Electron Microscope. Whether or not these specific images are useful in your classroom, this could give you the idea to possibly take images of the slides that your students are looking at. I personally think the guessing game would allow your students to think about the physical characteristics and appearances of the different cells and images they are looking at.
Microscope Image Guessing Game