Some, not all, off-road diesel still is not ULSD. You have to look for it, but can still get it, for now. What you do find is older fuel that is being sold to get rid of it. You are right that they do not make diesel with a higher than 15ppm sulphur content, but they still have a bunch of the 500ppm stuff in storage that they are using up in some off-road distributors. The ULSD stuff doesn't store well as it is a Petri dish for bacterias. That rust looking coffee grounds you find in diesels now is bacteria growth. It is a big problem as the higher sulphur content prevented it.