I think you are out of luck, I don;t think you can download it from anywhere else.
Microsoft Remote Desktop 8 Download Mac
Download this app from Microsoft Store for Windows 10, Windows 8.1, Windows 10 Mobile, Windows Phone 8.1, Windows 10 Team (Surface Hub), HoloLens. See screenshots, read the latest customer reviews, and compare ratings for Microsoft Remote Desktop. CoRD was a Mac OS X remote desktop client for Microsoft Windows computers using the RDP protocol. It's easy to use, fast, and free for anyone to use or modify. 2020-04-13: This project is defunct. Most people will be happy with Microsoft's clients.
Maybe also look into http://cord.sourceforge.net
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.
Download Microsoft Remote Desktop 8 For Mac
Microsoft Remote Desktop 8 Mac Download Without App Store
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