Found your message when visiting this site to ask for help. It's very unlikely any Fenwick might ever came from Ireland where I live and where there are just a few Fenwicks, no one from any old Irish family . Maybe some border reivers might have been part of the Scottish Plantations, so maybe try Ulster more than Ireland. Our name has its origins in Northumberland. But when I visited Australia some years ago, I dialed our name on the computer of the Convict Museum and.... got this information :
"Andrew FENWICK Age 25, sentencedto 14 years for desertion in Court Martialat Cork on May the 30th,1836, borninBerwick , married,one child, protestant,soldierand labourer,readsand writes. Arrivedin Sydney,05 01 1837, on the Saint Vincent".
At the time, I was suggested to get in touch with the First Fleet Association in Sydney.