Pleco has flash card sets for HSK at each level last I checked. Lots of sites and books in any bookstore will have practice questions from previous tests. The Hello HSK app is quite useful not just for the practice questions but for the detailed explanations (all in Chinese, but at level 6 you can handle it) of test question type and test taking strategy. You should be able to go down to the test centre directly and take practice tests too, just book a time with them.