Ok, fair point, apologies for being so cryptical - the measurement from brake surface to brake surface - the internal diameter and the external diameter too please.
19mm outer width on a Mavic clincher rim with 14mm internal. Same as a 700c.
More importantly the tyre spec - 23-571 or 650x23C.
Have you tried sourcing tyres from Dahon or similar - they do 24" & 26" I think for they're folding bikes - I was told to contact them when I was sourcing a 650c clincher but one came up on ebay as NOS so I snaffled that instead.