Finding full text of instruments (the actual test or measure, rather than a review or summary) can be a bit of a treasure hunt. Many instruments are proprietary (owned by someone) and require a fee. It completely depends on the instrument, though, so here are some tips:
Research articles using the test or measure will often include enough sample questions that you'll have a good enough sense of what the instrument is like. Some articles even include full instruments as an appendix at the end of the article, but this is not common. If you are planning on using the test or measure in a real study (undergraduate research included), you definitely need the full text. If research articles don't give you enough of a snapshot to understand the test or measure, you may want the full text.
Sometimes doctoral and master's students will include full instruments in one of the appendices at the end of their document. Skim through the table of contents at the start of a thesis or dissertation to quickly tell if there's a test or measure in an appendix.
Your subject librarian can always help you search!