It looks to me like you have all-vinyl/leatherette seats as was mostly the case for British Standards, unlike their continental equivalents which had the herringbone fabric cloth.
This can be sourced easily...but whether the colour will match, that is a different story.
I think you will find a standard seat frame without too much difficulty. In fact, if you're near London, you should contact Luke at Terrys Beetle Services in West London. He still has the remnants
of a 1958 RHD Standard from which he used to have all the interior with original vinyl. Unfortunately, the vinyl is cracked and hard because the car was left in the cold and wet weather for too long...
48REME wrote: