The Brothers Four
Between September of 1998 and October of 2000 The Brothers Four performed more than 150 times in the US and in Japan. It was the only time the group ever traveled around America by tour bus.
It still amazes me the group is going strong after 55 years. Some years the phone rings more often than others. Those years were one of those times.
A correction: The performance at NHK Hall was attended by 3000 people not 300.