Thorn Tree travel forum

Travelling overland and the Tibet travel permit

I am travelling through China on a one month visa and would like to make my way overland using a combination of bus and train to get to Lhasa. I am currently in Beijing, my next destinations are Xi'an, Chengdu and Kunming. From Kunming I plan to take the bus (following a suggested itinerary through SW China) to Lhasa. I am not interested in buying a train ticket from any of the destinations mentioned to Lhasa, but is there any other way I can get the permit? Or is it necessary to book a ticket through these travel agencies which includes a ticket to Lhasa? Any advice welcome :) Thanks in advance, Brett