Go to the channel under your developer account. Select Edit Channel, then select Edit Properties. From that screen, you should be able to select the channel stores you want the channel available in. Once you've updated those, you'll need to publish a new package (you can just republish the existing package) to push the changes.
My Channels: http://roku.permanence.com - Twitter: @TheEndlessDev
Instant Watch Browser (NetflixIWB), Aquarium Screensaver (AQUARIUM), Clever Clocks Screensaver (CLEVERCLOCKS), iTunes Podcasts (ITPC), My Channels (MYCHANNELS)
