You might have better luck just doing apt-cache search kernel-image
to see which kernels are available for installation from your current cache.
To search the unstable tree, first change your /etc/apt/sources.list to something like:
deb ftp://ftp.us.debian.org/debian/ unstable contrib main non-free
Then run apt-get update
which will download just the package names in those unstable, contrib, main, and non-free trees.
Then when you re-run apt-cache search <package-name> you'll see which packages are now in your apt-cache.