Do this in your irc client.
This returns the list of bans on that channel.
Copy it. Save it. Done.
If this IS what you want, and then you want to automate the process to happen periodically, then we are off to the races on figuring a good way to do so.
If you need to keep track of dynamic bans, give thought to Spike^^'s idea, too. They would appear in the bot's .user file, but not in the irc server's ban list using the command that I just posted. In other words, you might need both.
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