List/Data/Summary question

Goal is to have a summary sheet of which vendors were chosen throughout a purchasing project.

Sheet 1 is a matrix of all items to be purchased, listed by vendor (pulling from a linked master sheet). 

Sheet 2 is a summary of vendors being used. I need to summarize which vendors were chosen but do not want duplicates.

For instance: If I have vendor A listed 4 times for 4 different items, I only want vendor A listed once on a summary sheet, instead of four times. How do I do this? Ideally the summary sheet auto-populates as vendors are listed in the product matrix. 

Advice welcome.