I know there were quite a few 350X take-out engines floating around for a while. They just cut the exhaust, the wiring, and pulled the engine out. Many went to high schools and trade schools to use for small engine repair training, many ended up in the hands of private individuals (I had one, sold it last year).
Also, just like cars, the next model year is being produced this year to hit showroom floors late in the year.
With these two facts together, although I've never heard of "take-out" ATC250R engines like the ATC350X, I suppose it's not impossible. While a few complete 87 ATCs were sold in Canada, I suppose it's possible the bare engines might have been available in the states.