Don't know where you are located...but .. Mar-Quipt in Pompano beach Fl has been making custom arches for the last 25 yrs or so.... or Double R manufacturing in Ocala Fl ( mar-quipt former owner)
There are probably a few thousand places that make them in the US
Go to a search engine like www.google.com
search Stainless Steel radar arch
Start surfin for the one you want
Jason