This is probably due to shuffling everything around during the merger - they might be rotating aircraft in and out of different hubs now and adjusting their whole schedule to align with CO's. Have you searched for flights through EWR? There should be an early morning departure and high frequency to LAX from there.
Other than that, I'm not sure if there's too much you can do to stay with UA. Delta is pretty good about its morning flights, and there are ones around 6:00 or MSP and ATL, and DTW/JFK a bit later.

Also, when are you searching for flights? If they are more than a month or so out, the early departures might come back. Then again, it's probably better not to wait to book those if you need an early flight.