I have one that was Custom Made, to add a Front derailleur to a Brompton Folding bike ,

to be offset for a frame that has a telescoping seat post that passes behind the BB, so quite offset..

Custom is how things that are made in small quantities, for a specific need, get produced..



Your situation? Have you asked one of the many fine Bike Shops in the South Bay?

A possible Bodge : get an oversize Clamp for a regular 28.6 seat tube bike
and shim it outboard by the difference available in using the "Wrong size" say 34,9

have roughly 6mm that it can be placed off center..











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