There should be some way to access it through C and/or ObjectiveC, but exactly how is a different question. The Apple Developer Site has a pretty good set of documentation; you'll probably want to start looking here for stuff on I/O Kit and the HID related frameworks.

Unless this is something that's going to poll constantly I'd just cheat and run ioreg; it only takes six hundredths of a second to run according to my shell's timeing.