What's the longest you've had to wait for a parcel to arrive that eventually got there? Unregistered/tracked post really stresses me out.
I know, right? They really must think you're incapable of checking alternate sources.
Try just searching y!jp/rakuten/ebay, some yohji shirts often pop up for pretty good prices.
Look at Our Legacy shirting too, the fit is nice and relaxed and it's great quality. (http://www.ourlegacy.se/store/product/category-aw12_shirting/maison-shirt-light-border-off_-white not sure if it's linen or not, but it fits the guidelines you wanted apart from that.)