Many of the measurement tools you find will have been validated before they were named and widely used. Finding the original study that validated your tool can help you actually get a copy. You can use an internet search engine to try and find the original validation article like this one below:
Sometimes the best way to get a copy of the scale you want to use is to email the author of the original scale and request a copy or information about how to get a copy. The primary author's email address is usually listed in the details of the article.