Map of Tasmania?

I am new to DIVA-GIS but I have read the manual and tutorial and I am making progress. I want a series of graphs showing the occurrences in the Australian State of Tasmania of each of a number of species of a particular fungal genus. I haven't had any problems preparing the individual graphs (similar to that of the potato distribution in Bolivia, as in the tutorial), but the resolution that I have for the boundaries of Tasmania are very poor. I got it from downloading the administrative boundaries from the 'world' file on the DIVA_GIS website, as there didn't seem to be a file for Australia. Because of the huge scale, when I blew the map up to focus on just Tasmania (including the Furneaux group of islands and King Island), the resolution of the boundaries was very poor.
How may I obtain a better quality map of Tasmania that I can turn into a shape file? Once I obtain a reasonably good quality map, I will be using it repeatedly together with the occurrence data for each of ca. 60 species from the same genus.
Thanking you in advance for any help you might offer me.
David Ratkowsky
Hobart, Tasmania, Australia