Im not sure if I understand the need for silk touch on shears, don't they keep leaves in block form anyways?
Yes, but silk touch on shears is useful for mining glass, ice, and other such things, and it doesn't use durability.
If sam hasn't sold you the shears yet, I would like to say i have a enchanting shop at 19091 and i can easily put the enchants you want on a shear for you at no extra cost