Depending on how you scored in the practice tests you can decide what are the next steps. If you scored well, I wouldn't worry too much about it. While it is an important part of the screening process, if you did well in a couple of exams you should also do it "on the big day". My focus there would be timing and not just accuracy. You have less than 1 minute to answer each question, and it is important to be on top of your game and manage time properly.
If you feel you did not score well and want more practice exams, there are several resources online that you can use. These include jobtestprep, graduatesfirst, wikijob etc. All these give you access to a limited set of practice questions and then you can purchase more booklets if desired. Another option, albeit time consuming, is to apply to banking jobs which usually use SHLs as a first screen. Once you complete the application you should get the exams immediately.
Best of luck,