1957 Princeton Tigers v Harvard [16 November]
1960 New York [26 November]
1961 Stanford [December]
1961 San Francisco [December]
1964 Boston [15 May]
The list may be subject to change if more rugby union sevens tournaments are discovered.
The Daily Princetonian of Tuesday 19 November 1957 remarks at the end of a rugby article on the 1st team of the Princeton Tigers playing a match against the New York Rugby Club at Fitzpatrick Field on Saturday 16 November 1957… that Princeton Tigers 2nd team played a Seven a side rugby union match against Harvard; and that the Tigers won.
The Fairfield Stag newpaper has various entries of the Fairfield Rugby Club competing in the annual New York Sevens tournament at Van Cortlandt Park. The events are noted as the last Saturday in November.
One note of the fifth annual Sevens tournament of 28 November 1964 notes that 45 teams were invited to that year’s Sevens; the Old Blues club won the 1964 event beating New York rugby club in the final.
Not yet definitely sourced, however the implication is that the first annual New York Sevens was on 26 November 1960.
The Stanford Daily of 3 December 1964 noted that the Stanford University rugby club will play in the fourth annual Sevens tournament on the Stanford fields on the 5 December 1964. It notes that 30 teams will compete in the 1964 tournament. As this was the fourth annual tournament it implies that the first annual Stanford Sevens was in 1961, again probably December.
The San Mateo Times of 25 October 1961 notes that the Peninsula Ramblers Rugby Club will take part in the San Francisco Sevens tournament in December of that year.
The Fairfield Stag newspaper of May 13 1964 notes that on Friday 15 May 1964 the Fairfield rugby club will go to Boston to compete in a rugby Sevens tournament which was sponsored by the Harvard Business School.
Rugby union sevens teams from M.I.T., Dartmouth, Yale, Harvard, Brown and the Harvard Business School were also lined up for the tournament.