An online PET practice exam can be found at www.english-online.org.uk
At the top there are links for 2 tests:
Click on Test 1 and you have the choice of 4 skills in the exam:
Then click on the skill you would like to practice and the parts of the exam are listed. Click on any one of these and practice:
There is no Speaking practice but Writing, Listening and Reading are all there.