The problem with not being able to see the Slingbox Mobile for Andriod Marketplace are filters within Google's Marketplace. If you're using an unsanctioned operating system, in a country unable to purchase paid application, or have a rooted phone then you won't be able to see it within the marketplace. This is because the Slingbox Mobile is a paid, copy-protected application.
Available per country (http://www.google.com/support/androidmarket/bin/answer.py?hl=en&answer=143779)
Unavailable per country (http://www.google.com/support/androidmarket/bin/answer.py?hl=en&answer=138294)
Work around for Froyo Users (http://www.androidcentral.com/how-get-your-paid-apps-back-froyo)
Work around for non-rooted phone (http://www.google.com/support/forum/p/android/thread?tid=441baa3452369f21&hl=en)
Work around for rooted phoes (http://www.google.com/support/forum/p/android/thread?tid=2a55855a017b346c&hl=en)