I also see this as related to the topic since the topic was filling itemcache.wdb and that's what QuindoMa wants to do.
Besides that, I ve got two ideas:
Visit the AH, enter the following into chat, wait a bit and then scroll through the whole AH:
/script QueryAuctionItems("", nil, nil, 0, 0, 0, 0, 0, 0, true)
Install the latest version of my ItemDB: http://my.curse.com/downloads/wow-addons/details/itemdb.aspx
It has a build in PT3.1 browser and ctrl-clicking the search button will try to fetch all unknown ids of the set currently shown. Also will the buildin LibInventory-2.1 help a bit with populating your cache by forcing some API calls in specific situations that are known to be safe for item querys.