Am I entitled to the latlong coordinates of all specimens used in a species revision paper?
No - you're not entitled to anything. Authors may refuse to share because they want to control future publications arising from their data, either simply to inflate their own publication record or to prevent certain types of anlaysis of their data (see the 'data parasites' fiasco last year for an example of attitudes towards data sharing in some parts of the medical community - this, this, and others).

Alternatively they may simply no longer have the data. Nowadays this is less common, but if you contact an author about a publication from the 1960s it's pretty unlikely that any unpublished data is still in usable form.

Finally, certain aspects of data may not even have been recorded. Before GPS was widely used, accurate lat-longs of collection sites are unlikely to have been measured. As @Kara notes in the comments, it is not uncommon for the collection sites of older samples to be recorded at the country level.

This is why journals are increasingly adopting data-sharing policies (see BES, for example)

However, many authors are happy to share their data, and you lose nothing by asking. Good luck!