So is any body building a diesel bike thats OEM?
Yes and No.
Track 800 out of the Netherlands used same manufacture as the Smart Diesel engine (essentially same engine) and CVT system by CVtech out of Canada to a BMW shaft drive rear end. Unfortunately, his profit margins were eaten by sub contractors etc. so he closed all sales. Erik is still in business.... just on paper it seems. Some Tracks can be found in used market overseas.
There was a bike made for the Marines that was diesel also and some were shipped to the military. Not many. That company sold all its holdings to a well-known manufacturer in India and nothings been done with it even though they promised to at the time of purchase couple years ago.
Royal Enfield in India for decades sold the Taurus with a diesel Greaves engine.