... Doesn't help in any details but could explain why there is no record of William H Thornhill and Matilda's passages recorded to NSW
I was not aware that the couple were thought to arrive in NSW but I have now spent quite some time searching for any THORNHILL arriving in NSW 1856 – 1858. Judith has found the marriage in December 1856 (reply #19, 31 Dec. 1856 Worsborough Church at Darfield) and I agree, no need for passports for passengers moving within the realm of the British Empire.
So I can confirm that I have diligently searched my offline resources for any sign of the couple arriving in the Colony of New South Wales in 1857-1858. I have NOT met with success. Cando has already explained that The Colony of Victoria was hived off from NSW back in 1851. I note that the Colony of Queensland was not hived off from NSW until 1859.
Re 250 miles … that would be considered a very short distance to travel if you were a resident in NSW. The urban sprawl for Sydney covers a much larger geographical area than many other cities around the globe, and each of these large cities have their own unique burdens regarding costs, time, expenses, accommodation etc.
From Albury on the border of NSW and Vic, to Kingswood NSW (where the NSW State Archives are) is about 600 kms.
From Boggabilla on the border of NSW and Qld to Kingswood NSW is about 750 kms.
From Broken Hill near the border of NSW and South Australia to Kingswood NSW is about 1100 kms.
Greater Sydney Basin is perhaps around 12,000 km
2, and I think that’s almost ten times more than London, The population of Sydney is around half that of London.
Public transport in NSW is umm... well ... It would take me over six hours by public transport to get from my home to the NSW State Archives, and that's not including a walk of more than 1 km from where the bus sets you down to the front doors of the Archives office... If I were to drive, there's many a tollroad between here and there... I am sure there’s many RChatters who could share their local knowledge about their difficulties getting to/from their localities to the Records Office in Melbourne, Victoria. Just as we have read of the difficulties getting to London... these are hurdles ... But those details do not help our OP re the request for help finding William Henry and Matilda THORNHILL's arrival, when there's evidence of them at Beechworth which in 1858 was (and still is) in Victoria.
.... One place to try is 'The National Maritime Museum' in Greenwich, London UK holds a lot of records (Logs)on ships with detailed info the commercial/merchant ship staff on board and maybe passengers of that time period.
Here is the Resources Board for Australia :
http://www.rootschat.com/forum/australia-resources-offers/Within that board are sub-boards, including ones for the six colonies which became states in 1901 and the two territories.
Our OP has not been back online since 24 July, 2017 after joining just two days earlier.
JM