This is a Brand New in original foam IBM Model M keyboard, part 1391401 from 1992.
Here's how the IBM Model M keyboards were packaged. From what I was told, most of these did not have "retail" box packaging since they were just going right into service in an office, so they were just taped to foam and did not have a box, like this one. I read elsewhere that even IBM itself tossed thousands of unused and unsold Model Ms, so these are quite hard to find new.
These keyboards were factory taped to the foam as shown - I cut one side of the foam to show the top side of the Model M.
I can understand why new ones are in such high demand - there is a lot of gross gunk and hair below a majority of the used Model Ms from years of usage.