If you want to go to Linzhi, Tibet, you can contact the local eco-travel agency, which is directly under Linzhi Tourism Bureau. Don't worry, there is an office phone number 0894-583428 1, you can contact. I'm not familiar with the travel agency in Lhasa, sorry!
In fact, you can come in by train or plane yourself, and the travel agency behind will help you arrange it, but I think it is most comfortable not to join the group charter, hehe!
You can contact me if you need anything else.