Hi I do have a copy of the marriage certificate but no witnesses are listed which is odd. Thanks for all your searching 
Hi there,
Yes, that's odd not to have the names of the witnesses. May I please ask a couple of questions about that copy that you hold.

Is it issued by an official transcription agent? , and if so,
is it a partial transcription (you can pay for particular parts of the document to be transcribed, and alternatively you can also pay for all of the document to be transcribed.)

Is it the NSW BDM issued certificate? and, if so,
is it a recent issue, or was it issued say back in the 1970s? It is possible that the NSW BDM's practices in earlier decades did not include typing up the names of the witnesses. (I have several NSW BDM issued documents from 1970s, for marriages prior to 1856, and NO witnesses noted on the NSW BDM issued certs, HOWEVER,

the witnesses names ARE on the NSW BDM holdings, and have been included on the NSW BDM typed up pre 1856 marriage certs for several decades.
There's other possibilities, but if you have a NSW BDM marriage cert (or official transcription) and there's no record of the witnesses on that document, it is likely that ordering a new transcription will give you the witness names. That detail was recorded by the clergy when marrying couples in NSW from the commencement of settlement, and of course was a requirement of the laws and regulations of the various denominations, in the original parish register.
It is entirely possible that the NSW BDM holdings do not have the original details, and perhaps only hold a summary.

Sorry for being so long winded, BUT from the marriage certificate you do have, it will give you the name of the clergyman, the denomination (according to the rites of ...........) and where the ceremony was conducted. From that info you can seek out the original registration, and in many instances the original local parish registers are extant.
Cheers, JM