Custom Crazy announced recently that they have a limited supply of 'silver' weapons including the butcher knife, square cleaver, kunai, sai, knobbed mace, and handle type 'C'. Limited supply means once they are gone, they're gone.
Silver or no, the sais and kunais can be great additions to your ninja arsenal. With LEGO bringing the ninja theme back via Ninjago, it might be a great time to stock up.
You can see all of Custom Crazy's product at their online store.