He used to own an airline called "Trump Shuttle" that he had bough from the Eastern Airlines shuttle. That's where he got his 727. I don't thing he had a personal former airliner aircraft prior to that. It was pretty hard to pick up used 707's after the early 1980's, because the US Air Force bought most of the ones that came on the market to use as parts to upgrade its fleet of KC-135 aircraft. It was probably convenient that the 707's disappeared from the used market. They had considered reengining exising 707-300's with CFM engines and redesignate the upgraded planes as 707-700's, but their economists predicted that reengined 707 would reduce demand for new build 757's.