Apple - Can't find or use San Francisco in apps like Sketch

Initially, you had to have a developer account. Now anyone can download the font at https://developer.apple.com/fonts/ and install them on your system (using the font book app).

Now Sketch is satisfied and it won't give you any warnings about the missing San Francisco font.

The short [& even long] answer is no.

It's not only that it's only available to developers, it's that it is not licensed for use as a user font at all, in any way, shape or form.
Even developers are only licensed to use it for screen mockups etc.

See https://apple.stackexchange.com/a/208854/85275

Even if you unpack it, tweak it so it no longer appears as a system font & repack it, it would then be a different font & the substitution would happen anyway,

This guy is a hero - you can download the font here: http://www.developertown.com/apple-tvos-sketch-template

Or direct download: http://cl.ly/1N1k3i1L361h/download/SF-Fonts-August-26.zip