Stone Tool is one of the three skins released as part of the Stone Age coin deal. This skin was available for purchase in mid May 2017.
Stone Tool could be purchased for $9.99 in a deal that includes 16000 coins. It could also be purchased for $19.99 in a deal that includes the Fire Face skin and 1800 DNA. Stone Tool was not available for individual purchase and may not be available for purchase in the future.