For a great resource on various events that happened on Tu B'Av throughout history, check out Larry Domnitch's The Jewish Holidays: A Journey through History. Regarding singles events, he cites the fairs in 16-17th century Poland. On page 113-114, he writes:
In those days, matches were often made at fairs where the multitudes gathered. In the book Yeven Metzula by Rabbi Nathan Nata Hanover, the author describes how thousands converged upon the fair in Poland in the years prior to the Chmielnicki massacres (1648-1649). The open fairs of the summer were held on the seaside villages of Zaslow and Yerislav and attracted great numbers of people. The fair was a place of socializing, conducting business, and relaxation. It served as a brief respite from the difficulties of life.
Tu B'Av marked the end of the summer sessions in the yeshivas in Poland and thousands of students would converge upon the fair with their instructors. There, they studied with students from other yeshivas.
Naturally the fair was an ideal place for networking and the arrangement of marriages. Rabbi Hanover wrote, "Whoever had a son or daughter of marriageable age journeyed to the fair, and there arranged a match. There was ample opportunity for everyone to find their type and suit...hundreds and sometimes thousands of such matches would be arranged at the fair." [...]
The fairs in Poland were a substitute for the open fields in biblical times. The times, circumstances, and locations in which marriages were arranged have frequently changed and they continue to change. Diverse situations, however, offer the same opportunities for those in search of their of their bashert (destined one) and allow for the continuity of the Jewish people.
