Metal fabrication in complex stressed Shapes, one off, is very expensive. Fiber glass ditto.
Given you would need oem blueprints and specifications you need to be a lottery winner.
Assembly jigs and tools .. motorcycles are bad enough, and "new old parts" involve quantity to control prices. And most motorcycle bits involve casting, machining, and or tube bending.
Pure machining, from billet, if you have specifications, dimensions, tolerances, materials, and heat treating is doable.
Drop forging one off complex frame or body parts, finishing to factory like appearance. Oh man. linkages, assembly order procedures.
Things like wire harnesses, and getting a certificate of origin, ..