travel to Lhasa from Beijing

Hello!
I'm from Russia. Next month I'm going to be in Beijing. I've already got China business visa. I'd like to kniw is it possible to get Tibet Travel Permit for me (I'm going to travel alone).
Is it possible to fly from Beijing to Lhasa, to stay there for 2 nights, and than to fly back to Beijing.
If there is any travel agency in Beijing I can contact to halp me, please help me to find their contacts.

I'd be thankful for your reply.
Ekaterina