I'm using Ubuntu 9.10, and need to add some apt repositories. Unfortunately, I get messages like this when running sudo apt-get update:

W: GPG error: http://ppa.launchpad.net karmic Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5A9BF3BB4E5E17B5
W: GPG error: http://ppa.launchpad.net karmic Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 1DABDBB4CEC06767

So, I need to install the keys for these repositories. Under 9.10 we now have the option to do this:

sudo add-apt-repository ppa:nvidia-vdpau/ppa

See this Ubuntu help article for details.

This is great, except that I'm running this on a workstation behind a firewall which blocks outbound connections to pretty much all ports except those required by secretaries running Windows and IE.

The port in question here is the hkp service, port 11371.

There appear to be ways to manually download keys and install them on apt's keyring. There may even be a way to use add-apt-repository or wget or something to download a key from an alternative server making it available on port 80.

However, I haven't yet found a concise set of steps for doing so. What I'm looking for is:

1. How to find a public key for an apt-package (recommendations for resources which have these, and/or tips for searching. Searching for the key hash doesn't seem all that effective so far.)
2. How to retrieve a key (can it be done automatically using gpg or add-apt-repository?)
3. How to add a key to apt's keyring

Thanks in advance.