Hi Carlos,
Three members of the Launceston Walking Club attempted a private descent of the New River in December 2001, which almost ended in tragedy, and the story was told in Wild's Autumn Magazine No. 104. John McLaine, who wrote the article, is a forum member and could give you more information, but he has not been active here for a long time. In November 2005, he paddled up the New River almost to the point where he was injured, as part of a trip to climb the Provis Hills.
Details from WILD.COM.AU search:
Title: The Valley of Horrors (Feature)
Author: John McLaine
Publication: Wild Issue 104 (01 Apr 2007). Page(s): 42-46.
Description: Bushwalking and liloing trip account of an attempt to descend the New River, from Farmhouse Creek to New River Lagoon, which almost ended in tragedy, including map; New River Gorge, Crest Range; exploratory trip; evacuation; history
Location: Australia, Tasmania, South-west
Page 44 has a map of their trip which I have scanned for you, but you will have to get a copy of WILD 104 or read it in your local library to get the full story.