right, the maps for the pc version are added to your account by clicking a link somewhere on the web. the first was "hidden" in telltale interloper newsletter from july and the second is hidden on several mi fansites, like mixnmojo.com or the miwiki.net. these two are listed as maps #7 and #8 in the account. #1 should always be there and #2 is added when you claim the prize for #1.
the maps 3-6 are already included in the wii version.
p.s.: you should check the treasure hunting thread in the general tales section, you may find some links there.
Corn is no place for a mighty warrior!