When you say "shells," do you mean the empty brass casings that could be reloaded?
If the "official" data is not available, could you obtain ammo instead (perhaps by purchasing it from here in the U.S. and having it shipped to you) to satisfy the authorities there?
Sites like GunBroker offer this ammo from time to time, and I am sure that there are probably members here who would be happy to help you get the ammo you need from their own stocks. I got out of the caliber last year, unfortunately (and not willingly); otherwise, I would be happy to send you some myself.
By the way, 850 euros is about $930 -- a good price indeed for a Super 9 with the 9x19 barrel. The other site did not show a price but does show the three barrels with the gun.