What is a device used to slice tomatoes with in one motion called?
Yes, believe it or not... it's called a Tomato Slicer, but they are also sometimes referred to as a Tomato Saber. Which is a product name originally from the commercial company Price Castle.  

Although I agree with Stephie and janeylicious just include the additional keyword 'commercial' with your search.

Another option is that you can try the keyword 'Tomato Saber', this should also aid to a successful search.