Need graphics card for Opti 3060 SFF

Where can I find part numbers or somewhere I can buy a graphics card for the Optiplex 3060 SFF? Dell offers them as options on a new system:

• Nvidia GeForce GT 730
• ATI Radeon R5 430

Both of these are 2 x DP ports, which is what I need. How can I buy one of these cards?