Seeing as the original company was a 'publisher' and the current company is a stationary company, it may be that the publishing division was acquired by a larger publisher and their sourcing division was not part of the merge and was allowed to retained the name. If that is the case, any rights to the map should belong to the company that acquired the publisher. I would double check the copyright date on the map and consult with a copyright lawyer. Depending on the year of the copyright, the period covered varies. As I recall, anything published before the 1930's under copyright is now public domain unless the copyright was subsequently reinstated.

Your best bet is a lawyer, but knowing what became of the intellectual property rights of the publisher would save you time and money on that consult.