Here you can find numerous links to the websites where you can practise modal verbs.

MODAL VERBAS OF OBLIGATION, PROHIBITION, NECESSITY  and LACK of  NECESSITY.

Have fun!

http://www.autoenglish.org/modalverbs/ModalsObligation.htm

http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-67368.php

http://www.englishpage.com/modals/interactivemodal1.htm

MUST/HAVE TO http://www.englishclub.com/grammar/verbs-modals-have-to-must-not-quiz.htm

SHOULD/SHOULDN’T – http://www.eclecticenglish.com/grammar/Should1A.html