According to Aniplex, a 10min short anime of Gintama "Shiroyasha Koutan" will be released on September 30th. It was shown at Jump Super Anime Tour 2008 and had never been released as a DVD. It's a trailer of an imaginary Gintama movie. Gintama OVA shown at Jump Anime Tour '05 is also included in the DVD.
9Anime is the best site to watch Gintama: Shiroyasha Koutan
SUB online, or you can even watch Gintama: Shiroyasha Koutan
DUB in HD quality. You can also find Sunrise
anime on 9Anime website.