The message
from Dougie Nisbet contains these words:

On the other hand, if I could find a local timber merchant (just moved
into the area so still finding the local outlets) and told them the
dimensions would they be likely to cut a piece to size?

Take them a section, or cut a cardboard template and take them that. A
good woodyard should be able to match it easily.

--
Skipweasel
Pay no attention to that man behind the curtain.