You should assess an instrument's validity and reliability before you try to obtain its full text.
Where you find that data depends on whether the instrument is "published" or "unpublished."
Use This Flowchart to Determine How to Assess Your Instrument:
The Library Databases Can be Used to Find Assessment Information!
You can search for reviews of instruments using the library databases.
To find a review, search for the instrument name and include the word review, reliability, or validity.
After you complete your search, find articles that discuss reliability and validity.