The Royal South Australian Almanack 1839 does not list George Mawbey in its business directory, but does the following:
John Stuckey, baker
J Pitman, joiner and pianoforte tuner
John Reynell, landholder, 'Surreyville', 81, Rundle Street
Archibald Macdougal, printer
George Alston, accountant, 41, Rundle Street
Dingham and Harvey, merchants
Flaxman and Rowlands, merchants
John Forrester, victualer
Miss Nihill, ladies school
___ Williams, builder
E Baker, Adelaide Bazaar
John Crawford, builder
Clement Crispe, butcher
At the beginning of 1839 when this alamanack was compiled, it was not two years since the founding of the new colony, and there were already 620 houses and 5,000 inhabitants.
[Source: Royal South Australian Almanack 1839]

UPDATE 19-12-11
According the Royal South Australian Almanack 1840, John Reynell, was a director of the Joint Stock Cattle Company. It was established to 'supply colonists with the purest and most approved breeds of cattle, as well as butter and cheese at a moderate price'.
Mr John Stuckey, baker in Rundell Street, had been appointed one of their agents for butter.
Archibald Macdougall published the Southern Australian every Wednesday morning, price 1s.

No person or persons convicted in any court of justice in Great Britain or Ireland, or elsewhere, shall at any time, or under any circumstances, be transported as a convict to any place within these limits.

                                                    Constitution and Government of the Colony [of South Australia].
From its conception, the province (now state) of South Australia was an exclusive, convict-free zone.
All of the other colonies of Australia - Western Australia begrudgingly - imported convicts as a form of cheap labour.
The SA Colonisation Commission thought it could still supply free labour to land owners by attaching a levy to the price of land which would be used to 'carry' (transport) poor families from Britain.
Those eligible under the 'emigration fund' had to be 'real' labourers between the ages of 15 and 30 and married.
Single women could come if they were attached to a family, like an aunt.
On the arrival of these labourers in SA, they were not to be 'indentured' like the convicts (attached to a particular employer), but rather allowed to negotiate their conditions of employment with an employer of their choosing.

Free labour and no convicts means the colonists are protected from the enormous evils which result from the immorality and profligacy unavoidable in a penal settlement.

This was the situation in SA when George Mawbey was running his own business in Adelaide in 1839-40.
[Source: Royal South Australian Almanack 1839]