Join Date: Aug 2015
Location: DXB
Programs: AA EXP, A3 *G, LH SEN, SK EBG, Marriott Titanium, Hyatt Globalist, Hilton Diamond, etc. etc....
Posts: 3,348
No, ITA can’t do that. It will only show separate fares when they can be combined into a single ticket, which isn’t possible with your UA/AA scenario.
Kiwi, however, sells you separate tickets on a single booking, so you can use their search for cases like this. But you should still book directly with the airlines.