I bought that part a few years ago. It is (or was) still available new from a dealer. Be prepared for a price shock though. You probably can buy a whole used mower assembly for the price of that part. Things like that are brutally expensive new and usually worn badly if used. I suggest you also look carefully at the pitman straps that mate to the nubs on that housing to see if they are worn oblong. If so, I'd expect the nubs on a new housing to wear prematurely. That particular joint is one that needs to be checked frequently for proper tightness. Once slop starts to be evident, wear increases rapidly. New straps will also be extremely expensive. BTDT. Check with an AGCO dealer of NOS AC parts.
I don't know of any other options. Mine wasn't broken but the nubs were excessively worn (as were the mating pitman straps such that a tight joint could not be had. At the time I toyed with idea of a weld build-up on the nubs but the machining would be impossible for me due to the taper involved and having it done professionally would be cost-prohibitive. Of course that would still leave the wear problem with the straps. Maybe you can cobble together something but in the end, I decided to bite the bullet and buy the NOS parts since I use the mower regularly.
PS: don't forget the thin hardened sleeve in the bore of that housing that the bearing rides on. It's like a speedi-sleeve without the flange. Mine was broken into three or four pieces. That sleeve does NOT come with the housing - it's a separate part.