On Wednesday, 24 October 2012 13:11:04 UTC+1, Jim Hawkins wrote:
Does anyone know of any firms that can design and
manufacture small Fresnel acoustic mirrors

No - because Fresnel doesn't work in "small". For optics, a convenient size is (optically) "large", so they work. For acoustics, a sensibly sized gadget is going to be (acoustically) small, relative to wavelength. So your gadget is going to suffer from so much diffraction as to stop it working.