Most parts houses don't stock everything they sell. It's their ordering policy that can screw you . If their vendor has a minimum order or more likely offers better prices on larger orders then orders will be combined. Chances are you are waiting because the order for your clutch wasn't even placed until a purchasing agent had the volume to make it convenient for them. Then Bav Auto assumes complete shipment from their vendor.
Having once worked in the parts business I can tell you most will try to accomodate a "vehicle down" order if they are aware.