Not sure on KTM delaers in Argentina (so this post may not be so useful to you!) but I do know that there are a few in Chile. Santiago for sure has a dealer, the importer in is Chillan (about 400k's south of Santiago) and I've just ordered 2 air filters form the dealer here in Puerto Montt (they will come overnight from Chillan). I also noticed he had a pair of OEM Scorpions in stock though the rear was 156,000 (about $300!) I paid $100 for a Metzler MT20 (or 21, I can't remember now) in Puerto Montt (same deal, was shipped from the importer in Chillan) and my mate has just paid about $200 for a tyre in Coyhaique (shipped in from Santiago).
So if you doin't have any luck in Mendoza, my advice would be head to Santiago or Chillan. When we were in BA I saw a 140/80/18 Scorpion A/T on a shop shelf so for sure they should be available in Argentina.
Like I say, I'm in Puerto Montt, heading south for Futulefu to meet back up with my mate Jase then up to El Bolson and Bariloche. Let me know if you need any more help.