That will be difficult. Those straps were unique to that watch, only came in yellow or red and many people found them a 'bit fiddly' to wear and use. Good luck....
Unfortunately the OP hasn't been here in almost 3 yrs now so its unlikely you will get a response. 🙁Did you find a solution? I’ve got exactly the same issue, Dunhill have declared that they will no longer manufacture the strap so I am thinking I may have to 3D print a rubber one somehow