EDIT: Though I missed it on the first read, this Character Builder update also includes the assassin multiclass feat. It's called Shadow Initiate.
One of the few flaws I found on the Assassin class (released exclusively for DDI last month, and commented here) was the lack of actual enchantments for the new type of magic item they presented for the class: the Ki Focus.
The problem was not unsurmountable, as it was easy to assume how a basic, 'Magic Ki Focus' would work. In addition, Mike Mearls (the designer of the class) made a post in a non-official forum suggesting to allow any enchant that was available to all weapons to be applied to Ki Focuses, as a temporary house rule. That was good enough for me, but many people was concerned by the lack of official rulings, and the question remained of how we would handle this on Character Builder, when the class was finally released there.
The class has been finally released on CB, and there's good news on the matter: 'Ki Focus' appears as a new magic item type, and the most basic enchantments (plain vanilla 'Magic Ki Focus' +N) are available to take. They also appear in the Compendium, as you can see here.