Little chance of getting a bespoke item off the shelf nowadays but when we had dr350's at work we made them from 1/4 plate welded up or in the past I've bought a secondhand rack and altered it then got it powder coated.
Last one was using a s/hand rack from a 1981 gsx750 on a 1995 import 400 katana.
The welding and fabrication took about 1 1/2 hours from start to finish.
Look on that site at item 110847179961 and it will give you an idea, try starting with a rack from any similar vintage twin shock (I assume your dr is twin shock)