Hi Sonia, well you are very blessed to have all that research from Jackie. Wow. So that establishes the candidates for "your" Thomas pretty well. It still is possible this list does not include him, but more likely your" Thomas is on this list somewhere.
From Jackie's list, I pulled together a smaller, starter list of five boys named Thomas who are of about the right age and who have a father Thomas Thomassen (or similar). The father for "your" Thomas was said to be a Thomas Thompson, so for the moment, we'll proceed on the hypothesis that this is correct.
Note that for some of the boys on Jackie's list, the father is not noted.
Below are the five boys and their families in the 1865 Norway Census. I have transcribed just the main points in the census records.
The next step is to trace the movements of each of these boys to see if one of them emigrated at about the right time. (Remind us, when did "your" Thomas emigrate?) Jackie and other volunteer researchers can help you with this, if you request the help - I cannot, I do not have the expertise.
And yes, I like your idea of getting every possible record that you can within Australia. Every drop of information may help. For example, in Norway, a naming pattern would be for Thomas to name his first-born son after his father and his first-born daughter after his mother. He may not have followed this practice! However, if an immigrant did follow this, it can help to connect him with his original family. Another example - if you could discover that Thomas had a sibling in Australia, that too could help make the connection back to the Norwegian family. Etc. etc.
1. Thomas Eid Thomas. Son of Thomas Thomass. Born about 1855 in Mandal; 1865 census link did not work for me.
2. 1865 Census in Holden Thomas Thomass. Age 43 Born in Widdeseid. [By the way, Thomass. = abbreviation for Thomassen] Mari Hansd. Age 42 born in Widdeseid[Hansd = abbreviation for Hansdatter] Hans Thomass. Age 15@13 [sic] Born in Bøe Thomas Thomass. Age 11. Their son. Born in Holden. [Born about 1854.] Elsa Maria Thomasd. Age 5 born Holden. In household also is Ingebor Johannesd. Age 72 born in Holden; something about her being fattig/poor…
3. 1865 Census in Horten Anne Thommas widow Thommasen, age 46, born in Skjeen Ingeborg Vilhermmine Thommasen 18, d [=datter/daughter; ug = ugift/unmarried] b Horten Anna Thommasen 15 d born inHorten Thommas Thommasen age 12 born in Horten Anders Thommasen age 5 born in Horten Hendrijette Augusta Thommasen 3 born in Horten
4. 1865 in Naes (needs Norwegian ae) Thomas Thomas. Farmer age 40 born in Naes Prgj. [Thomas. = Thomasen] Kari Eriksd age 36 born in Naes Prgj[Eriksd = Eriksdatter] Thomas Thomas. age 12, son, born in Naes Prgj --all the children born there Erik Thomas. 10, son Fingar Thomas. 8, son Barbo Thomasd. 4, daughter Also: Knud Niels. [=Nielsen] 31 “Husf inderste” [= housefather’s lodger?] Kari Thomasd. 38 his wife Barbo Knudsd. 2 their child
5. 1865 Lyngens Tomas Tomassen age 48 born in Lyngen Bereth Andersdatter 48 born in Lyngen Ole A. Tomassen, their son, FISHERMAN, 21, born in Lyngen Tomas J. Tomassen 13 their son, born in Lyngen Nils H. Tomassen 6 born in Lyngen Anne M. Tomasdatter 19, helping her mother in housekeeping, born in Lyngen Inger K. Tomasdatter 16, helping her mother born in Lyngen Elen Malene Tomasdatter 11 born in Lyngen Bereth M. Andersdatter 65