Perhaps one of those illegal streaming boxes might have it on them? They seem to be all the rage getting lots of media attention right now, but dont pay the idiot tax by buying one locally. They are on aliexpress for a tiny fraction of what they are locally. Dont ask on here or any other respectable forums about getting it working tho as most places take a dim view of accessing pirated streams.

Other than that, easy and legal, no. It is listed on sling.com as an available channel, will need an unblocker to view the page and get the streams. Not sure on paying them for it either as I only used a free trial and then gave up.

Will be the US version of the channel which is quite different to the AUNZ one, for one it is HD and looks good. The shows are newer and a different range of them. If there is something in particular you want to watch then check a guide for US nat geo channel to see whats on.