Tbh I'd consider you fortunate to have even found a key at this point. Remember that the keys you're looking for are now nine years old, and there has certainly been interest from others in obtaining them. A thread seems to pop up here every now and then about them. Supply and demand principles apply, so if you're not willing to bite the bullet on those Amazon listings you'll just have to keep trawling through every retailer you can find in the hope there are others (I suspect online ones would be better). You're not going to find one for $10.