Vespa PK 50 XL PLURIMATIC ELESTART - contrast spring

Hello! Do you know where I should buy new contrast spring for my scoot VA52T? And where is it located in the engine or transmittion? I think, that this spring is on the lower shaft, behind the clutch. Or have someone parts catalog or service manual for this scoot? (I have just original parts catalog with pictures for PK 50 XL - no plurimatic.) Thank you!