Depending on which OS you are using and/or which version of Windows you have or are emulating, will determine which of the below linked files you should get.
If you are using/emulating Windows XP or Windows Vista you should only need the below files:
Microsoft Visual C++ 2005 Redist (x86)
Microsoft Visual C++ 2005 Redist (x64)
Microsoft Visual C++ 2005 SP1 Redist (x86)
Microsoft Visual C++ 2005 SP1 Redist (x64)
Microsoft Visual C++ 2005 SP1 Redist ATL Security Update
Microsoft Visual C++ 2005 SP1 Redist MFC Security Update
Microsoft Visual C++ 2005 Redist (IA64)
Microsoft Visual C++ 2005 SP1 Redist (IA64)
Microsoft Visual C++ 2008 Redist (x86)
Microsoft Visual C++ 2008 SP1 Redist (x86)
Microsoft Visual C++ 2008 Redist (x64)
Microsoft Visual C++ 2008 SP1 Redist (x64)
Microsoft Visual C++ 2008 Redist ATL Security Update
Microsoft Visual C++ 2008 SP1 Redist ATL Security Update
Microsoft Visual C++ 2008 SP1 Redist MFC Security Update
Microsoft Visual C++ 2008 Redist (IA64)
Microsoft Visual C++ 2008 SP1 Redist (IA64)
If using/emulating Windows Vista, the following files might also help:
Microsoft Visual C++ 2010 Redist (x86)
Microsoft Visual C++ 2010 Redist (x64)
Microsoft Visual C++ 2010 SP1 Redist (x86)
Microsoft Visual C++ 2010 SP1 Redist (x64)
Microsoft Visual C++ 2010 RTM Redist MFC Security Update
Microsoft Visual C++ 2010 SP1 Redist MFC Security Update
Microsoft Visual C++ 2010 Redist (IA64)
Microsoft Visual C++ 2010 SP1 Redist (IA64)
If you are using/emulating Windows 7, Windows 8, Windows 8.1 or Windows 10, also get these in addition to the above files:
Please note that for these three links, the files for both 32 bit and 64 bit versions of these can be found on the page after you click the 'Download' button and must be 'selected' via a checkbox before the actual files are downloaded to the computer.
Microsoft Visual C++ 2012 Update 4
Microsoft Visual C++ 2013 Redists
Microsoft Visual C++ 2015 Redist
Microsoft Visual C++ 2015 Redist Update 3
Microsoft Visual C++ 2017/2019 Redist
For the two versions of Visual C++ 2017 Redist and/or the 2019 Redist, the link goes to a general Visual Studio 2017/2019 page. To find the two files associated with each, scroll down the page until you see 'Other Tools and Frameworks' section. Under that section and at the bottom is where you can select and download the x86 and x64 versions of Visual C++ 2017 Redist or 2019 Redist. As the 2019 Redist is still very new, this link will probably change when MS fully releases the Visual C++ 2019 redists. For now, this is where you can get those files if you don't have them.
Also of note is that the 2015, 2017 and 2019 Redists are all connected. The newer versions will overwrite the older ones unlike the previous version of the C++ Runtimes, so keep this in mind.
Although Directx 9.0c comes packaged with the Game Client, in the event you need to reinstall it for whatever reason without having to also reinstall the client itself, the SDK file is provided for download below: