Microsoft Internet Explorer for Mac is not available for the latest OS X versions (beyond OS X 10.4) as it was effectively replaced by Safari in 2003. As the Wikipedia page for Internet Explorer for Mac explains:
As a result of the five-year agreement between Apple and Microsoft in
1997, it was the default browser on Mac OS and Mac OS X from 1998
until it was replaced by Apple's own Safari web browser in 2003.
On June 13, 2003, Microsoft announced that it was ceasing further
development of Internet Explorer for Mac and the final update was
released on July 11, 2003. The browser was not included in the default
installation of Mac OS X v10.4 "Tiger" which was released on April 29,
2005. Microsoft discontinued support for the product on December 31, 2005 and removed the application from their Macintosh downloads site
on January 31, 2006. Microsoft recommends "that users migrate to more
recent web browsing technologies such as Apple's Safari."
Your best bet is to download the Windows version of IE and run it in a Virtual Machine (using something like VMware Fusion or Virtual Box).
Alternatively, the OSXDaily article on Internet Explorer for Mac the Easy Way: Run IE 7, IE8, & IE9 Free in a Virtual Machine describes a way to do this (I've not used it myself, but this does appear to circumvent the Windows 30-day trial period by using snapshots and possibly to comply with the EULA you should purchase a Windows licence and use that in a VM with a downloaded version of IE, as above, instead):
We’re going to walk you through how to install Internet Explorer 7, 8,
or 9 in a virtual machine running Windows, directly in Mac OS X – for
free. This is achieved by using the freely available VirtualBox
software from Oracle, and combining that with free Internet Explorer
testing virtual machines from Microsoft, the trick is converting these
free IE vm’s so that they work flawlessly under OS X (or Linux,
technically), and that is all handled automatically with this method.