There are DDC pumps made by Barrow and Bykski. I don't think there are any major differences between barrow and bykski, both would fit in a ddc housing. There are two main grouping, a 10W version which is supposed to be quieter and equal to the EK-DDC 3.2. Then there is the 17W version which is supposed to be equal to a normal DDC pump.
I don't think they sell the pump by itself. The different model number refers to the pump top and pump housing (aluminum or plastic, etc), but they share the same pump.
You can see the Bykski pump in Optimum Tech video on the iceman reservoir pump combo. You can also see the barrow pump in Optimum Tech video on "my dream cpu waterblock on exist".
TL;DR Alterative to EK-DDC 3.2 should be Barrow or Bykski 10W pump. Model difference is only because of pump top or housing. Note the 17W version approximates a normal ddc pump, see Optimum Tech videos