Try John Zalcberg in the GI Oncology department at Peter MacCallum. He has been an author on GIST research papers and trials. http://www.petermac.org/patcar/
Also...
Sarcoma department at Peter MacCallum http://www.petermac.org/patcar/
Dr Grant McArthur
Jayesh Desai was a fellow at Dana-Farber working on George Demetri's sarcoma team before returning to Melbourne in 2004. He is very knowledgeable about GIST and has co-authored a number of papers on GIST.
He is listed under the Peter MacCallum Sarcoma Service Team
http://www.petermac.org/SarcomaServiceTeam
He is also listed under the Ludwig Institute for Cancer Research
http://www.licr.org/contact/ContactSearch.php?uid=6606
Another GIST Specialist at Peter Mac is John Zalcberg. Dr. Zalcberg has a couple of titles: Executive Committee, Chief Medical Officer, Director Haematology and Medical Oncology. He participated in the Phase 3 Imatinib trial in GIST. He was also a co-author of the 2007 "NCCN Task Force report: management of patients with gastrointestinal stromal tumor (GIST)--update of the NCCN clinical practice guidelines", that is a major standard of GIST clinical care.