According to Wikipedia, 3-inch disks were not only used in Amstrad and Sinclair home computers, but also by the smaller British home computer makers Oric and Tatung, as well as Sega and Yamaha. However there are no details about which Sega and Yamaha models those might be...
https://en.wikipedia.org/wiki/Floppy_disk_variants#3-inch_%2...
It's interesting to hear Tatung described as "British", but for their computers that's an accurate description. I know the same 'Tatung' from their iconic Taiwanese electric steamer[0]. While Tatung is a Taiwanese company, their British research lab designed the Tatung Einstein TC-01 home computer with a 3" Hitachi floppy drive.
I highly recommend this newsletter on the Tatung electric steamer. Likely worthy of its own HN post.
0: https://newsletter.yunhai.shop/p/-taiwan-and-its-steam-cooke...
The Oric Microdisc was a rare peripheral, rather than being built into a computer like with the Amstrads.
It was originally promised for the Oric-1 (with no details about what form it would take) but details were initially vague, with it being announced as a 3" drive only around the time of the release of the follow-up model (the Oric Atmos). It finally arrived on sale around a year after the Atmos, only a few months before Tangerine went out of business. I can't imagine many were actually sold in the UK, though some probably turned up in France where the Atmos was a bit more successful.
There's a bit of info at https://www.computinghistory.org.uk/det/31261/Oric-Microdisc... so it definitely did exist (unlike several other peripherals promised by Tangerine over the years!)
The Sega model is seemingly the “Super Control Station SF-7000”, an add on for the SC-3000 computer.
I think some of the early Roland rack mount samplers had 3" Quikdisk drives too.
S-220 maybe. By the time of the S550 they'd switched to 3.5" like everyone else.