Z,Here's what the Roher book states.
All '32 passenger cars came equipped with a B-1430 rear spare wheel carrier(rack) was ordered at extra cost. This option included the B-18618 straight across tube, which was not available separately, except through service.
The B-410 sedan delivery used part B-18169 which was the luggage carrier cross tube minus the vertical flanges.
They're out there but might be harder to find than I had anticipated.
Z