This link is for a model of a No. 24 Limber made by Bull Models. To make the model perhaps they were able to locate an original limber and if so, hopefully they will be able to help you.
http://www.militarymodelling.com/news/article/trailer-artillery-no-24-limber-in-1-76/21579
Bull Models don't have their own website but their contact details are on the above link.