Not sure why the FFG WotR Collectors edition forum has been moved, but it can be found here:

http://agameofthrones.com/edge_foros_temas.asp?efid=163&efcid=1

Why is it so difficult to find?

I don't rightly know, but I imagine it might have been considered redundant. Dividing the forum into one for the regular version and one for the collector's edition did not make a whole lot of sense after the initial release, where people reported things to do with components and physical aspects, rather than gameplay ones. Once that sort of traffic dies down, it's just silly to have two forums for the same thing, where visitors of one may not look into the other. Additionally, the WotR forum sees so little traffic that dividing it only guarantees even less traffic.