HunterCO...yes they make it in shorter lengths...but it's more expensive of course because there standard 9mm barrel is cut at 16". If you order it for Olympic...yes you can order dirrect just an upper...you can specify order options that are not on any list. There would be a $50 custom fee...no parts fee to just cut it down. I've heard of a few even being cut down to the 7" range.
Be prepared to wait if you want anything "custom," wait times have been almost 1 year.

Because it is a blow back type action...no gas system....you can have a local gun smith cut it back and re-crown the barrel to any length you want....faster delivery and you won't have to wait a year for the upper.

Of course if it's legal...like you are installing a bla.bla.bla. or it's a SBR...bla.bla.bla. we all know the laws..........

Just CYA ya know.