L1011 and DC-10 no longer are in service domestically in the U.S.
If you care for flying a A340, consider flying PR
(I know, the latter is located in Canada ...).
Many / Most of the B744's flying domestically on UA
had been re-positioning flights between their hubs. So, these would be the routes to see them nowadays, but as you say, very rarely.
Try to look into flights Westcoast to HNL
or transcons from IAD
Carpe diem ! Life is too short to waste your time ! Keep in mind, that today is the first day of the rest of your life !