Got an e-mail from Jonas at Mura Minatures (http://www.muraminiatures.com) the other day - after I'd bought a few of his excellent 6mm Japanese houses and shops. He'd seen the post on Japanese castles. The castles he mentions below come in a variety of sizes (including 1/300) but are well worth checking out the links. As wargaming centrepieces for the period, I'm sorely tempted to try at least one! Jonas' e-mail (with all the links) is at the bottom of the page.
He's also got some tutorials on how to build a Japanese period buildings in 28mm.
Anyway, Jonas' e-mail...
Nice blog! I noticed that you mention the Doyusha castle kits, and I've actually built two of them. They are very nice, but sadly a little bit out of scale for 6mm. However, they make awesome "background" scenery to put in a corner. I've bought my kits in Japan, but even though most retailers add some shipping, they are not as expensive as you might think. Hobby Link Japan has only a few of them in stock (http://www.hlj.com/scripts/
Here's my Edo castle from Doyusha: http://s174.photobucket.com/
and my Gifu castle: http://s174.photobucket.com/
If you take some pictures of your painted buildings I'd love to put them on my website, if you are ok with that.