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.