Go all the way to the end of the beach, then about 100 to 200m around on the rocks. Be there for the bottom of the tide and look for small rock pools at the low tide mark. Hand digging may be required, so have some good gloves and be prepared to get wet. Some rock pools will have spiky sea erchins in them and blue ringed octopus are also there( I found one)so be caire full. Try to get to the bottom of the hole you choose to work as most of the stones will be sitting on the granite at the base of the hole.
Good luck.