Hi Jacky Lee
The best place to start looking for Thomas Hanson's records would be the State Records of NSW
http://www.records.nsw.gov.auYou can search the catalogue to find the appropriate records that you are looking for. As Thomas was a convict there would probably be something in the Colonial Secretary's Correspondence as well, relating to his gaoling and admission to the Asylum and then you could send to the State Records for them. If I can get to the library tomorrow I will check the fiche.
Gladesville Asylum had it's own cemetery so Thomas may be buried there, as his death is fairly early, 1847.
If you enter Gladesville Asylum into a Google search, there are quite a few hits, including images of the grounds.
Hope this helps you out
Cazay