STK kart data

Hi all,
I would like to modify the regular Tux kart to please my son. Where can I find blender readable data for this kart ? I looked in the share directory of STK, but only found .b3dz that I do not know how to convert to blender format.
Regards
I would like to modify the regular Tux kart to please my son. Where can I find blender readable data for this kart ? I looked in the share directory of STK, but only found .b3dz that I do not know how to convert to blender format.
Regards