Here you have a few sites where you can work on relative pronouns:
http://www.miguelmllop.com/grammars/mygrammar/relatives.pdf
http://www.english-test.net/esl/learn/english/grammar/ei039/esl-test.php
http://www.ego4u.com/en/cram-up/grammar/relative-clauses
http://www.tcet.com/EAonline/FlashedESL/fe-relative.html
