Sorry for the delay, but I’ve been away for a week in Wales (and, yes, it was sunny!).
I would try Ransomes at Ipswich as a starting point, but don’t hold your breath. They used to have a couple of people there who used to specialise in Iseki products and they would go the extra mile to find things if at all possible, but they both took early retirement three or four years ago and there is nobody there now who has a knowledge of the history of the brand.
I’ll have a dig about and see if I can come up with any alternatives for you.