In this rig diagram of John Frusciante's rig circa 2001, one can see a Fender Dual Showman.

Jimi acquired new Fender Dual Showman amps in 1968. He would typically use three of these 100 watt amps with cabinets containing two 15-inch J.B.Lansing speakers. These amps were used in the studio, and on the 1968 Experience tour, together with Marshalls and Sunn. Source Jimi Hendrix: Electric Gypsy by Harry Shapiro.

Jimmy Page uses the Fender Dual Showman amplifier, as detailed on his official equipment page.

http://www.jimmypage.co.uk/equipment.htm

In the background of this photo taken at Abbey Road studios John can clearly be seen plugged into one of the two Dual Showman amplifiers given to the Beatles by Fender in the 60s. Try not to stare directly into Yoko, its bad for your eyes!

Used between '64 and '66

Used on the You Made Me Realise EP, as mentioned in this May 2018 Sound on Sound article.

“When we did the You Made Me Realise EP, we didn’t really have many instruments,” he says. “I had a Fender Sidekick 65 that I used quite a lot. They were transistor Fender amps and my friend had lent me his [Fender] Dual Showman valve amp. But I actually preferred the hardness of the transistor amps."

Pete Townshend’s use of blackface Fender Showman amplifiers and Fender 2x15 cabinets on the American tour in August–September 1967.

In this pic you can spot two Fender Dual Showmans

In an interview with Tom Rice for the Gear4music Blog titled "Yes 'Close to the Edge' 50th Anniversary - Steve Howe EXCLUSIVE Interview," guitarist Steve Howe explains his use of the Fender Dual Showman: "I’d already got a Dual Showman. I don’t know that I had two of them. But what I did have was some sort of Super Twin that had four speakers in it – and it was a big thing. Usually, the front pickup would go in that Double Twin and the Dual Showman would take the back pickup. So that’s how we recorded it. Pretty much, (Tales From) Topographic Oceans was the same thing. Somewhere in the late ‘70s, we started using round stages and the Dual Showmans were just too big a cabinet. So I switched to Twins, which the front-of-house engineer just loved because he said the 12’’s were much better for projection than the 15’’s in the Dual Showmans. So I went to Twins."

"Those were red knob reissues of the Dual Showman. I still have a few of those. They’re really cool amps. I know Robben Ford plays those and there are a couple of other people who swear by those amps. There’s a Fender twang to those amps that’s really kind of cool."

In this image, Don Felder can be seen with a Fender Dual Showman behind him, just to the right of his Marshall JMP 2203. He used this amplifier live with the Eagles from 1976 until 1980. It was used in conjunction with the Marshall JMP on the Eagles' 1980 tour.

Eddie Hazel used the Fender Dual Showman amplifier as his preferred amp in the 1960s, as detailed by Angela Jamoso on Guvna Guitars.