There are quite a few places to obtain nos. You can try
dougstubes,kcanostubes or thegearpage, These are all great sources
to find nos tubes at a great price. Hope this helps you out.
No it doesn't have pre-installed NOS, but you can ask the
showroom guy from where you get it to install the NOS, or you can
manually install it after you buy it, at the best of my knowledge,
the easily available nos sets in markets are 2x, 4x, 8x, and 10x,
10x is the most powerful.