Paul Revere and the Raiders.
My mother told me once that back in the 60s, she and her friends made a petition at their Catholic school to make thePaul Revere look the school uniform. 
There’s a particular photo of the Kinkis in their red hunting jacket phase that I was trying to locate, but I couldn’t find a decent version so this one will have to do.
And image-googling the word “Kinks” can throw up some, uh, interesting pictures.
“Kinkis”???
:smack:
The Wiggles!
…I’ll go away now.
Before they found fame with ‘You Really Got Me,’ The Kinks went for the whole leather and whips look. (This picture is from early 1964.)
:dubious: If you count this time last year as “way back when”. (And yes they {and their anamatronic stand-ins} still wear identical clothing.)
Those links don’t work.
What about Slipknot?
That makes me think of The Residents, who also wear masks and dress alike.
The Super Furry Animals used to come on in identical Sasquatch outfits at the end of their shows. http://www.nme.com/artists/photos/photo/21014.htm
Their new thing seems to be glow in the dark spacesuits: http://www.nme.com/news/112957.htm
Cool. 
The last time I saw them touring was long ago. It gladdens me to hear of them still going strong. Musique, non stop.
Boys II Men used to do that. I think they stopped around the time of their final album.