Wikihow is the part of wikipedia where you get the "How to Manuals".This has manuals on many topics .
Wikihow also contains manuals on Origami.At present wikihow contains 50 articles on Origami.The Orgami structures manual available now are not very complex .The manuals are uploaded by users.Keep searching in wikihow.May be you can find the manual for the origami structure you are searching for.:)
You can have a look on the Wikihow Origami Manuals here.