Perhaps it is too late to be helpful, but zebedee and I have found some info about our French convict ancestor at
http://anom.archivesnationales.culture.gouv.fr/bagnards_doss...I can't find a Chappin or Garnay convict between 1860 and 1890, but the spelling could be different. Worth trying!
State records has a list of former French convicts living in Sydney in 1885. There is a "Henry Chappin, libérée, tailor at Loise Pitt street". I don't have the page which would contain Garnay.
There are some mentions of Henri Garnay in newspapers on Trove.
I hope this helps you.
Lyn