If you don't find any software, most generic TNC/packet software that will work with TNC-2 protocol will work for accessing the modem. Using the command line commands, you should be able to set the hardware to the correct mode. For RTTY, you should be able to setup using a dumb terminal like Hyperterminal and then PERM the setup. Sure, it will power up in RTTY mode but if that is what you want, you're in like Flint!
Do you have the manuals? You will need these to get all the commands to use (providing you don't have them memorized
I had a copy of KA-Gold s/w (came with my KAM) but last time I tried to use it, it kept asking for the registration number which I did not have and would not work. Sorry, I no longer have any Kantronic stuff at all except scans of the KAM and KPC-3 manuals.