Just put a new belt in the gt monday when my waterpump went out. Use the codes scarpash gave or try and fish the old one out of the trash. Its not a rare item, I was able to find a place in my town with them instock (amazing for my town!).
As for the pulley OGTS has them and so does opels unlimited last time I checked. Or you can call TGSI and get a set of 'power' pulleys.