http://www.englishexercises.org/makeagame/viewgame.asp?id=3233
http://www.ego4u.com/en/cram-up/grammar/conditional-sentences/type-3/exercises?02
http://www.better-english.com/grammar/con31.htm
http://web2.uvcs.uvic.ca/elc/studyzone/410/grammar/3cond1.htm
http://www.impact-english.com/members/Grammar_Practice/Always/test-grammar/gr_prac_form-Cond3.htm
http://www.englisch-hilfen.de/en/exercises/if_clauses/type_3_statements.htm
http://www.english-grammar-lessons.com/thirdconditional/exercise3.swf
http://www.englishgrammarsecrets.com/thirdconditional/exercise5.swf
http://www.redcamelot.com/camelot/exercises/SEPT26/Grammar/Conditional%20Sentences/Level%201.d.htm
http://www.perfect-english-grammar.com/third-conditional-exercise-1.html
http://www.bnv-bamberg.de/home/ulrich.koch/flg/englischinteraktiv/ifclauses3a.htm