First of all, did you TNOC your OS when you installed?
If not, you will need additional hardware.
This can be a TTL level converter, Arduino, embedded Linux device with TTL serial port, or any other device that you can use to send stuff to your nspire over the serial interface.
If you don't have anything of this and can't wait for Ndless3.1, then yes, you will have to buy something.