I have a used centre without a sprocket, which is in good condition. No ridges on the bearing surface, just a little staining. £23 including 2nd class post.

If you go to facebook marketplace and put Ariel Arrow in the search box, you'll find a couple of gearboxes for sale.( One with the rest of the case as well...)

Morning John, if the part number on the inner face is 47-7014, it's most likely from a 250 BSA or Triumph. I've just sold one on ebay for a £10 but it had been repaired a little,

Hi David, I think it used to belong to a guy calledMalcolm Bell.He was the London branch Sec in the 80's, and also the AOMCC Social Sec for a few years. He lived in Brixton and drove a London Bus for a living. After being mugged 6 or 7 times.... and burgled a few times too,( but he did live in a squ...

I'd also recommend Newman Cams, they're in Farnborough, Kent. They do the Ariel club's Sq4 cams and followers, and many vintage cars and bikes,including one offs.