Should be fairly easy to find a replacement. Leave your base mounted to the roof, remove the pivot screw I mentioned, then take that piece to your local auto parts store and match it up with one of theirs. It may be chrome instead of black but who cares. No one is going to see it. Here's one but I'm sure you can find one cheaper. I would try to find one with a spring at the end so that it will bend out of the way if you get hit by a low flying branch or while at the Mickey Dee's drive thru.
https://www.amazon.com/Motorhome-Trailer-Antenna-Adjustable-Mounting/dp/B007HRVK94