Ram Compatibility Question

[cspj]

Hello. I have a gigabyte 870a-ud3 board with 1 corsair 2gb cm3x2g1600C9NX ram, and I want to get additional ram, but I cannot find this exact model anywhere. What is some other models that will be compatible, and how can I tell?
Thanks in Advance.

Other specs:
Phenom 2 x4 965
radeon 5850
windows 7 home premium

 

[omnisome]

Here is what is necessary for mixed-RAM to be stable/compatible:

-Same brand
-Same voltage
-Same speed
-Same DDR


I honestly don't think it needs to be the same model to run in concert with the other.