A scan of a receipt from a Sound City music store in London from January 1967 shows that Jimi purchased a "1966 Marshall Supa Fuzz" pedal.

This receipt was auctioned off. The description of the auction reads:

Music Memorabilia: The Jimi Hendrix Experience, collection of original Sound City receipts 1966 - 1967. Jimi Hendrix receipt & carbon for Marshal Super Fuzz 20/1/67, Noel Redding loan receipt carbon for Fender Tele Bass 24/1/67 signed Noel Redding & Tony Garland, Chas Chandler - invoice for 3 sets Fender light gauge 1/11/66 & a carbon for the same dated 27/10/66

Original auction page here.

Used while recording 2011 Black Keys' album "El Camino".

I use fuzz pedals, but I’ve never used a distortion or overdrive pedal -- just boost pedals. The Shin-ei Companion Fuzz and the Marshall Supa Fuzz are my favorites.

One with OC75 transistors was sold on Reverb.com by Crazy Plum FX in 2017, as documented by this November 4, 2017 Facebook post.

I'm selling my original 1968 Marshall Supa Fuzz once owned by J Mascis - thing sounds great. The whole story is in the listing on Reverb. Good price for a rare pedal not counting the fact that J owned it. I used this one and one other SF I own as examples to make the limited run Ark Royal pedal.

https://reverb.com/item/7054151-marshall-supa-fuzz-1968-gray-excellent-condition-oc75-owned-by-j-mascis

Used from 1967-1968 on stage. Before he changed to the Uni Vox

In the provided photo, Chris Squire is shown using a Marshall Model 1975 Supa Fuzz pedal during Yes' performance at the Crystal Palace Bowl in London, England, on September 2, 1972. The pedal's enclosure, identifiable by its more rounded edges, confirms it as a Supa Fuzz made between 1968 and 1972, as evidenced by the image provided. Photo taken by Michael Putland.

In this image one can see Ron Ashton's Marshall Supa Fuzz next to a Wah pedal. Pay attention to its shape, a very distinctive kind of shape. Marshall Supa Fuzz has a shape all its own. It resembles Vox Tone Bender shape just a little bit. Marshall knobs are placed on the higher part allocated with the noticeable slope in this cast body.

In a YouTube video titled "Analysis: Steve Hackett / Genesis Revisited Soundcheck Interview," Steve Hackett discusses using the Marshall Model 1975 Supa Fuzz pedal.

Mike Rutherford used a Marshall Supa Fuzz pedal on the song, as detailed in a Mixonline article by Tim Morse. The article mentions Rutherford's use of a "Marshall fuzz" through an Acoustic amp to achieve a distinctive sound. Given that the Marshall Supa Fuzz was the only fuzz pedal made by Marshall in the 1970s, we can confidently conclude this was the specific gear used.

In this Rig Rundown, JD explains that he uses a late 60's Marshall Supa Fuzz, on loan from a friend. JD explains that it's always been his favourite fuzz tone, especially hearing players like Pete Townsend who are famous for using it.

The Marshall Supa Fuzz also became the inspiration for JD's signature FarmlandFX Pedal made by Brian Farmer, which also appears in this Rig Rundown.

This pedal can be seen in one of Pauls instagram posts. Pauls version might be an older model but it is the same pedal.

In an Instagram post by pablosnowpatrol, Paul Wilson is shown with a Marshall Model 1975 Supa Fuzz, highlighting his use of classic fuzz effects pedals.