/var/lib/dpkg/available
i recently got an error from aptitude that /var/lib/dpkg/available was missing…
i found a file named available-old under /var/lib/dpkg and someone on a forum suggesting that, in case of a corrupt or missing “available”, you should simply do “sudo cp available-old available”
it has worked for me, although i’ll never know where this came from…

available-old is a content in d directory