It is not possible to download a DirectX 9.0C compatible graphics adapter. Graphics adapters are hardware components. As such, users cannot download graphics adapters. However, it is possible to purchase a new adapter that supports DirectX.
DirectX is an application programming interface that multimedia applications and video games use when rendering visuals and playing sound effects. Although DirectX 9.0C is an older version, downloading the latest DirectX version will also install DirectX 9.0C features.
Windows Update should automatically install the latest version of DirectX. To check whether or not your system has the latest version, press Windows+R, type in dxdiag.exe and hit Enter. Windows should open the DirectX Diagnostic Tool. Wait for the tool to gather information about your system, and check System Information under the System tab.
As of December 2015, DirectX 11.2 is the latest version. If Windows Update hasn't installed the latest version of DirectX on your system, you can install it manually. A free download of the latest version of DirectX is available on Microsoft's website. Make sure your graphics adapter supports the latest version by checking the website of your GPU manufacturer.
All modern graphics adapters support at least DirectX 10 and up. As of December 2015, the Geforce 210 is NVIDIA's cheapest offering on the market and supports DirectX 11.