I've looked into a bit further... The event
is available to usermode apps as showkey
detects it (I get keycode 69), however I was
unable to getch() it. It may be terminal
specific, and you might have better luck
searching the web for relevant information
than I did.
Thanks for the help! After some more searching and taking a look at the showkey sources, I was able to recreate most of the functionality of showkey in Perl (at least enough to capture numlock presses). I've posted an example program here in case anyone else is interested.