I'm sure I read that Sneaky Leaves are out of production now. So if shops don't have stock the only thing I could suggest is ebay (internationally might be your best bet).
@sonofsammo is correct they went out of production quite awhile ago. You’ll be hard pressed to find genuine sneaky leaves anywhere.
It pains me to suggest it because the group is full of incompetence and dreadful people (and run by one too) but if you use Facebook the SniperOps group have got some really good tips on making fake leaves look more realistic in their files section.
My personal choice is to get to site 20minutes earlier and use natural vegetation; it looks spot on with a bit of practice and as it dies off between games gives really good depth.