I would get that OEM e-bay trailer hitch, then add the electrical harness component that's missing. TerminatorX5 posted that harness link as well, so harnesses can be had. Another option to explore is this here.
P.S: And, yes, Bingo: there are a few for sale. Can't post the link with the results, because the URL won't work, but you have to do the search.

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Stable: e92is, e46 M54B25, e83 N52, e53 N62 - sold, e39 M54B30 R.I.P.