I would think they'd be very limited , if anything, available for next month. River cruising is so popular cruises are booked out 12 months or more in advance in alot of cases. We booked feb 13 for june 14 and now there isnt anything available on that cruise date, but thats for France. Last year we booked in january for an august cruise on the Danube and were lucky enough to get the last cabin.
Avalon Panorama, Magnificent Europe, Budapest to Amsterdam August 15 -29th 2012
Avalon Scenery, Grand France , Cote D'Azur to Paris, 30th June - 8th July 2014
Avalon Creativity, Grand France, Paris-Normandy Beaches-Paris, 8th - 15th July 2014