just search for the type of ndless you need as the same type as your os for example lets say i have a ti nspire cx cas (which i actually do) with an os of 4.5.0 i would search on ti planet.org for ndless4.5.0 and download it directly to my calc.
p.s. don't try to charge your expensive ti nspire cx cas using a school compurter especially if you have multiple things plugged in i did and my usb port melted.
An excellent place to find programs and games is on a website called ti planet.org no space in between the ti planet.org this website won't let me post links for some reason.
p.s. If you can't speak or read french you will want to use google chrome and right click the page and select translate to English, it usually works