Buying train tickets from Amsterdam to Cologne in February

Hi
You should recheck, there is at least 1 per hour. I know mornings there can be more per hour.
Use db Bahn, as the German railway runs these trains

Using the Deutsch Bahn site: http://reiseauskunft.bahn.de/bin/query2.exe/en/ I found many trains per day and a couple that are nonstop. I was using the 14 February to see what's available and to check prices. Were you per chance using Rail Europe which usually doesn't offer as many trains and usually costs more?

As noted, Cologne and Amsterdam have multiple rail connections per day. It isn't necessary to buy in advanced, but you can save a substantial amount of money. And don't buy from RailEurope, buy directly from the rail operators (Deutsche Bahn, Thalys, NS, etc.)

I would suggest booking directly with ICE/db bahn. I booked with the Dutch rail NSNL international and could not book seats. I had to contact NSNL for the coach/seats as they did not appear on my emailed ticket. Yes, there are many trains daily to choose. Make sure there are no connections as it adds time, so it's worth the money to get ICE tickets. As far as costs, the sooner you purchase the better the rate. More popular times the price goes up as tickets get purchased.

You must be using RailEurope. They only show one train daily from Amsterdam (8:02) to Cologne (10:45). The problem with RailEurope is that they are a travel agency that offers not all the trains available (there are a lot), but only the trains that they want to sell you, the most expensive ones, and at a markedup price. You can buy a full fare ticket for that train from the Bahn for 68,20€ (about $70) per person (vs $88 from R/E). If you are willing to commit to a non-exchangeable, train specific ticket booked up to 92 days in advance, you can get a ticket for 19€/person. A ticket from the Bahn has better refundability than a RailEurope ticket and can be sent as a .pdf file with no shipping charge.

Quick note to say that Thalys do not run trains between Amsterdam and Cologne - to use them you would have to change at Brussels which is a less direct route.