By tournament:

1974 Algida Sevens
1980 Dorigo Sevens

The list may be subject to change if more rugby union sevens tournaments are discovered.

Algida Sevens

From The Official History of the Melrose Sevens by Walter Allan:

The Algida side from Rome were the first organisers of a seven-a-side tournament in Italy in 1974.

Dorigo Sevens

From The Official History of the Melrose Sevens by Walter Allan:

In 1979 Carwyn James, the then Dorigo coach, persuaded his club to launch a sevens tournament. London Scottish, captained by Mike Biggar, won the first event in 1980.