Haha, I don't mind doing a bit of leg work in order to find an answer for you. I actually popped into an auto electrician on the way home today and spoke to a very knowledgeable guy there. He said that there will be a small module under the dash (driver's side) which controls the door beeper and headlight beeper, and all you have to do is simply unplug the module and the beeping will stop.
Apparently there is no wire as such coming off the ignition barrel as it is all controlled through the fuse-box (unfortunately there isn't just a single fuse you can pull out either as it would service more than just the beepers). What year is your Corolla anyway? He said that on the later models they have a slightly more complex module that controls almost everything, which makes it a bit trickier to disable.
The best thing he said to do would be to get down on your hands and knees while the door is open (while it's beeping) and locate the module by listening to it. I just tried doing that on my 1993 Corolla and the beeper definitely gets louder when you get your head under there, unfortunately I can't see up under the dash because all the plastic is still in place, but it sounds like it's right near the ignition barrel. Might be a fun little project for you this coming weekend, lol. Let me know how you get on when you get around to it

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P.S. Yep, they do say 'mate' here, although it probably originated in Australia

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