If it is a good mower then any light engineering workshop that does jobbing work could knock you up one in a couple of hours.
Whoever made the Ariens Zoom and Swisher both fabricate their own spindle housings from some heavy walled tube it is nota difficult job.
I am sill waiting for that end on bottom shot to see if the Great Dane housing will fit.
And Dane used the same spindle housing as JD does on their commercial ZTR's
All of the aftermarket parts suppliers do a pile of spindle housings, usually called Jackshafts, all you have to do is look.
The catalogues are all on line
I do not have it in my hand so I cannot tell you that Countax part 123456789 will fit .
I have to measure & compare .
A mobile mechanic such as myself or a workshop that repairs mowers rathe than a glass front retail outlet will probably be able to find one that will fit.
I don't even have a listing for Better Outdoor blades in the specialist blade catalogue & they have over 100 machines listed .