When you register for the exam, you'll get a booklet with a practice exam and suggested study materials.
Don't know of any practice exams (besides the DSST fact sheet) but if you get a copy of "Criminal Justice today" By Frank Schmalleger and used the DSST Criminal Justice Fact Sheet to guide your study you will have no problem with this test (i used the book for both criminal justice and intro to law enforcement). Here's a link to the criminal justice fact sheet which also includes a few "practice" questions http://www.getcollegecredit.com/NEWFACTSHEETS/Criminal%20Justice.pdf Good luck.