I've not seen anything like that--even a diesel motorcycle is uncommon, as small diesels are heavy and expensive , compared to a gasoline engine. I would say that a scooter/moped is just too small and light for any of the current diesel engines. And then to sun SVO means some method of preheating the oil, maybe a seperate tank to hold diesel to start it with, etc.
Just recently a diesel motorcycle came out, but there are very very few. If you DIY it it is possible, but my main concern would be learning more about the emissions of the little diesel engines (which are more likely than not older)...Though I wouldn't know where to go with this.
There was a time when you could get a 10hp air cooled, supposedly EPA certified, Yanmar clone (engine in article) shipped to your door for ~$600, but I'm pretty sure there's been enough international pressure for the common outlets to stop displaying them, and given how the one-off industry works in China, there might not be any more.
royal enfield makes, or at least used to make and sell a diesel motorcycle that ran fine on bio-diesel, but other then that I don't know of any that are in production and avalible outside of the millitary.
as for a scooter, no one makes a diesel scooter or moped, and if you go on a moped forum you will be told that it can't and shouldn't be done, I would guess that retro fitting a diesel on to a vehicle that size would dubble it's weight so insted of it weighing 150 pounds, it would be more like 300 pounds, as the engines are heavy, and increased vibration would require a stronger frame, heavier suspension, and befor you know it you have something that is built like a tank and moves about as fast.
also, you can buy a brand new high quality 2 stroke moped starting at $1,000, if you want to buy a small diesel engine budget no less then $1,500 just for the engine, and expect it to weigh 80 pounds.
now I've thought about building a trailer with the engine and a generator on it to power an electric bicycle, but for the cost, it would make more sense to invest in lithum batteries, and you would have a 100 mile range with less weight and it would be silent.
I got to ride a freakin' minibike with a 6-hp single cylinder Chinese diesel engine and it was a hoot! If you swallowed a nickel back when you were a kid, it'd shake 5 pennies out of you today... solid mounts didn't help, rubber ones could only be better. We beat the poop out of it for most of a day, and it still hadn't used 1/2 gallon of #2 diesel. I'd be using one today if it was street legal, but the California laws forbid it.
The other drawback was that I smelled like a kerosene fire.
And a good start. If it's produced and sells well, the big boys might catch on. Imagine everything from mopeds to boulevard cruisers to touring bikes being powered by diesel? Or a big V-twin Harley diesel? H-D, you may use that idea with only a tiny bit of compensation to me.