Sorry to hear that. I hope you catch those low-lifes.

Have you contacted die-cast collector clubs? They may have members in your vincinity that can also keep an eye open.

These links might help:
http://www.bamca.org/
http://www.matchboxclub.com/
http://toynutz.com/
http://matchbox.zsebehazy.com/
... and some link-lists:
http://www.faldix.de/index_eng.html
http://www.shabbir.com/matchbox/mbsites.html
http://modelcars.mbeck.ch/links.php?lang=e
http://www.modellautohomepage.de/linksa.htm

I will check the ebay pages, too. If your cars were sold to a clever crook, they might turn up on foreign ebay pages.