[@Aristo]

Nice pick-up on the problem with silver there, my friend! TV shows and Movies like to forget just how soft a metal silver actually is.
As for the weapons, perhaps the remaining silver-bound weapons are left from the olden times, where metalwork was a more common product.

Also, perhaps another metal could be harmful to these creatures? Titanium would definitely be strong enough in cutting off heads, let's be honest. A titanium-silver alloy could maybe work. (Not sure if that's actually doable, but it's a thought either way.)