Help with Ferrari 641/2

Help!  I've dug out an old Tamiya 641/2 to build whilst locked down.  The kit and the decals etc are all perfect but the tyres seem to have broken down, the rubber has gone all misshaped and hard.

Does anybody out there happen to know if there are tyres available as a grade up part or have a set they don't need? I've searched the web and can't find any anywhere.