Thank you once again to PrueM and vowgirl

I looked on "A gift to the Nation" site, have tried sound ex and still find nothing that is available on line, so that might mean a trip to Canberra for me, a few files that have matched eg: family names as next of kin etc, have not been examined yet!
John Darcy was born around 1880-1885 depending on which source it comes from, he was married to my grandmother Sophia Simpson on 26 Oct 1928, but there is a small chance that this may have been a second marriage.
The only other boys that that could have served as the sixth brother are Fredrick Gordon Darcy b1888 and Edward Charles Darcy b1898, all boys were born in Lauriston/Kyneton/Victoria to James Patrick Darcy and Jessie Darcy (nee Christie).
If it was Edward I can understand why I may not be able to find the records, as he would have been under 21 and I don't think that my ggrandmother would have willing let her youngest son be the sixth to go of to war, but at the same time she may not have reported him if he did (long story).
All service records have now been found for the following:
Darcy. George Edgar Service Number 1628
Darcy. Francis Patrick Service Number 3344
Darcy. Percy Service Number 5635
Darcy. Thomas Raymond Service Number 7221 & V10848 served WW1 & WW2
Any suggestions are greatly welcomed!
Cheers:)