Make some mock up ones out of HDF(high density fibreboard) nice and cheap, use saws/chisels etc to get the shape you need drill the holes so you make a exact copy of what you want, then any decent machine shop should be able to do these using your pattern.
Take your time and do it right, as alloy brackets wil only be as correct as the hdf ones, could use mdf if you want but get better detail with hdf.
tabetha