I think you are out of luck, I don;t think you can download it from anywhere else.
Maybe also look into http://cord.sourceforge.net
Apr 21, 2015 Hey Guys, I'm looking for a way to download the new MS RDP client for Mac from outside the App Store. I have looked online for the.dmg but all links lead back to the App Stor. SOLVED Microsoft Remote Desktop Client for Mac V. 8.0.15 - Microsoft Remote Desktop Services - Spiceworks. Conveniently download all previous versions of Remote Desktop Manager along with its documentation. Download Previous Versions - Remote Desktop Manager Features.
Why don't you try downloading it on your computer and see if you can extract the file from the download? Right-click and show package content.
Remote Desktop
PS: Is that: https://www.microsoft.com/en-us/download/details.aspx?id=465 the right client?
I can't test it since I don't have a MAC at work.
or this one: https://www.microsoft.com/en-us/download/details.aspx?id=18140