I just checked, there is the non-stop ICE from Amsterdam to Cologne from Deutsche Bahn, which is available for 34 or 39 Euros on 6 April. Leaves at 07:04, 08:04, 10:34, 12:34, 14:34, 16:34 or 18:34. The one at 18:34 is 29 Euros, the one at 16:34 is 49 Euros in 1st class.
This is all available on bahn.de - so not sure where you have been checking.
What I don't understand is the "Brussels" in the thread title - do you need to go to Brussels? and when? Or did you just think you had to go via Brussels if you need to go from Amsterdam to Cologne? This is not the case.