Hi everyone and thank you for your replies.
It didn't seem possible for us to source clay from the ground here. We live at the base of a mountain, the soil is rich, but we have found no clay. It is also only accessible by boat which we have to take into consideration with anything we bring over.
After scouring the internet more for ideas and possible solutions, we found a company called Clayworks
http://clay-works.com/ and had a really good talk with Adam who runs the company with his wife. He was really helpful and very knowledgeable about building rocket stoves, and cob structures.
We have ordered backing coat clay mix from them, and a clay plaster for the outer layer finish, which is being sent directly to us from Cornwall.
Excited to get it all completed now