Fabio - sorry to hear about this ... it does happen once in a while. You can try contacting AFV Club and see if they'll send you replacements, but that will take quite some time.
Another option is AM parts. A company called PSP used to make a set of tires and wheels for the Long Tom. R&J Enterprises in the U.S. list them but I'm not sure of availability. Here's the page they're on, about half way down.
http://www.rjproducts.com/Catalogs/PSP_Models/PSP_Models.html
Best of luck
Happy Modelling and God Bless
Robert