You can get a spare from the parts department but the cost is out of control, $570!!! I wrote Acura about it and said it was a big mistake to leave it off as they put it on all other 2017 MDX units except the front wheel drive version, where it is a lower cost option.
I ordered my parts on line for a lot less, under $200 and a 15 min install. Probably think we don't want that anymore then a hitch to mount a bike rack on. They are out of touch with their customer base.
Do you know what size bolts are used to hang the spare tire hoist? I purchased the hoist, but of course it didn't come with the bolts..Attached are photos of my 2017 MDX Sport Hybrid. Looks like the mounts are there for the hitch, without having the hitch in front of me its hard to tell but it looks like it would clear the muffler. Spare tire was not included, I ordered parts on line, winch, lug wrench, wheel and tire, all under $200, less then 15 minutes to install.
The motors are internal in the differential, it in now way physically interferes with a hitch mount.
I did additional photos that should answer all your questions: you can see that the mufflers do not interfere with the hitch mounts,
the differential and motors are all in front of the cross member and have no impact on the hitch mount, I also show the differential and rear motor housing. I trust that this clarifies this for everyone.