If you have the exact title of the test, do a search in Google using the title. You may find the complete test as a pdf or appended to an article for free.
If you find the test at a site that asks you to pay $$$ for it, first try some of the tips in this guide or ask a librarian for help.
If you don't have a title, just a topic, you can try a search like this (where self esteem is your topic):
self esteem test OR measure OR scale OR questionnaire OR survey -site:.com
NOTE: When using tests straight off the Web, you must confirm that the test was developed according to established principles of test construction. Only use tests that include the source of the test (sometimes called its "reference") and its scoring key.
The source will look like a citation, like this: Heatherton, T. F. & Polivy, J. (1991). Development and validation of a scale for measuring state self esteem. Journal of Personality and Social Psychology, 60, 895-910.
And the scoring key will look something like this:
Scoring: Items 2, 4, 5, 7, 8, 10, 13, 15, 16, 17, 18, 19, 20 are reverse-scored. Sum scores from all items and keep scale as a continuous measure of state self esteem. The subcomponents are scored as follows: Performance Self-esteem items: 1, 4, 5, 9, 14, 18, 19. Social Self-esteem items: 2, 8, 10, 13, 15, 17, 20. Appearance Self-esteem items: 3, 6, 7, 11, 12, 16.
The websites below were chosen from well-known organizations and universities that provide source information.