I have bought Khukuris from The Khukuri House, but in person, not online.  They have stores in Thamel and Ekanta Kuna.

The quality is pretty good.  I would say they are genuine because they also supply khukuris to British Army.  I believe their factory is somewhere in Bhojpur, so most of the khukuris are Bhojpurey style - short and broad - which is the most prevalent kind.  I did not see many Sirupatey khukuris.  Those are bit longer and slimmer -  mostly found in Paachthar area.

They also have really good collection of Kothimara khukuris - the decorative kinds that are given as gift to the British Gurkha Majors who are retiring - with regimental insignias.  But the silver on the cover - or daab - tends to tarnish over time.

All in all, I would recommend Khukuri House.