The pre 1870 period is challenging
Bobby De La Rue,
As you would know, in his book The Numeral Cancellations of New South Wales
, Hugh Freeman has John Sands with the contract from 1863 until 1870. John White also names John Sands as the contractor during this period.
In 1870 Hugh mentions the contract then going to 'newcomer' John Thornthwaite.
In fact, John Thorn(th)waite had the contract in 1863 but it was cancelled - apparently due to 'bad work' - and awarded instead to John Sands.
Legislative Assembly questions were reported in 'The Empire' in January, 1864:
Despite the prior engraver's 'anonymity' in both Freeman and White, it appears that the original contractor was probably Hugh Carruthers (an engraver who worked as a butcher) then J. C. Thornthwaite who, according to Basset Hull, was engaged for a number of projects from 1850 - including postal stationery and 'silver and copper tokens'.
Finally, Basset Hull quotes 1850 correspondence from the Post-Master General to the Colonial Secretary that shows payment to Hugh Carruthers and J. C. Thornthwaite for 'the obliterating stamps for various post offices'.
Hugh Carruthers returning to engraving in 1858: