Buffalo WZR-HP-G301NH
From DD-WRT Wiki
The Buffalo WZR-HP-G301NH is a router much like the Buffalo WZR-HP-G300NH.
[edit] DD-WRT on WZR-HP-G301NH
It has been reported that DD-WRT can be installed on the Japanese version of this router by web upgrade.
After reading the above, see Where do I download firmware? for links.