-
Just cog or freewheel an option?
https://www.sjscycles.co.uk/freewheels-single-speed/?teeth=24
-
If it has to be a cog to go on a freehub body then chop up a cassette? Single cassette cogs might be a bit narrow based if your freehub is ali but at that size there'd be plenty room to do something like sandwich a couple smaller cogs around the big one, drill a few holes through all three cogs and bolt them together.
-
Does it have to be from the UK?
http://www.endlessbikes.com/products/anodized-kick-ass-cogs/Could you not use a different chainring to get your required gear?
Anyone know a source of ss cogs bigger than 22t in the UK?