Where to buy valve springs

I have a Hatsan Gladius .22 long and I recently installed a Robert Lane regulator into the air cylinder and set it at 140 BAR. Even after adjusting the hammer spring a number of times to find the optimal tension for the hammer spring, the amount of air being used per shot was approximately 4-5 BAR. So I'm guessing the air cylinder valve isn't closing fast enough and I think I need a heavier valve spring.
Where do I order one and does anyone know the valve specs I would need to place an order.