If I've read your post right, you want to have two ratchet pieces. One the standard length and an additional piece which is longer, as per your image.
If it was me I would buy an additional ratchet piece from G&E (if available? not listed on Edinkillie...). I would then take it to a competent local metal fabricator and ask them to extend it by cutting off the top slotted section and (TIG) butt-welding in a fresh section of aluminium alloy of the correct dimensions to extend the length by the amount desired.
The Grunig piece might not be cheap but nor would asking a machine shop to recreate one from scratch. And at least you know it'll fit. The work as described above might sound a bit drastic but would be a piece of cake for any suitably skilled person.
Will ask around for recommendations for you. (I'm near Embra and know people who will know where to go)