Odds are you are going to need quite a lot of visual inspiration when designing costumes for stage productions. The sub-pages in the image section of this guide will help you get started searching for images in a variety of places, some you may have thought of and some that may be new to you.
You should not restrict yourself to looking at costume, clothing and fashion resources. Inspiration can be found in a number of places such as
While Googling images on the internet can yield some good results, don't be afraid to get creative and try something new.
Try a Creative Commons search for images you can adapt and reuse: https://ccsearch.creativecommons.org/
Try the New York Public Library's Digital Collections search by color: https://www.nypl.org/research/collections/digital-collections/public-domain
Or try one of the many online image resources listed at the links below.
Leon Bakst, 1922, Costume study for Nijinsky in the role of Iksender in the ballet, "La Péri"
The Hunter College Libraries provide access to several image databases. These databases allow you to search and download high-quality images from a variety of subject areas.