I contacted the steel compagnie in the UK (Dave's hint), and they directed me to an other compagnie.
So that is work in progress.
But I will keep you offer in mind Robb.
What was interesting is that they did mild steel tube in the elusive 9/16" size, which was used on the front stand (on the thick side) and the lower pannier support brackets not to mention Matchless rear mudguard stays, all of these have been made from stainless in the past because no one could get mild steel.