We have not yet come across a photo of the Snow White plastic viewer. However, Hake's did offer at auction a lot of six of the eight numbered 9" x 12" original artwork scenes from which the slides were created.
Also included in the lot were two additional pieces of artwork on aged stiff paper, each a pencil drawing of Snow White with the text, "Correct Head And Expression".
Images via hakes.com.
An Alice in Wonderland Viewmarx slide viewer can be seen over at Matt Crandall's Vintage Disney Alice blog. It is molded in the shape of the White Rabbit's house.
Peep hole on the back and the slide changer button on the bottom.
Non-Disney viewers were produced for other cartoon favorites including these three Hanna-Barbera examples.
Image via Heritage Auctions.