This link tells me what I must use for AS923 in Australia, and this tells me the frequencies to use.
My gateway (RAK7244) runs the Semtech packet_forwarder program. By default it does not support this band, so I need to provide it with a new config.json file. I could hack something myself, but a tested file must exist.
It would be very helpful if someone could point me at this.
Emphasis mine:
Actually what is says is
In Australia, The Things Network uses both the LoRaWAN AU915 band plan and (more recently) the AS923 bandplan. See https://www.thethingsnetwork.org/docs/lorawan/frequency-plans.html. Your region can use either one of these (or both).
For AU915, we use Frequency Sub Band 2, also known as channels 8-15, or 916.8MHz through to 918.2MHz.
For AS923, use AS920-923, aka AS1 aka 922.0 - 923.4MHz.
And further down:
In Australia, we use the 915-928 MHz frequency range with a maximum Equivelant Radiated Isotropic Power (EIRP) of 1 watt. In general, if you use AU915 or AS923 compliant LoRaWAN modules, you will be complying with the standard.
Note that US modules cannot be used in Australia. Although the US also uses 915 MHz, the actual band is wider than ours (902-928 MHz) and it is illegal to use the lower part of the band in Australia.
You have the option to use either of these and I beleive the RAK7244 can support either band.
There is a scism if the use of the bands in Au, in part driven by history, early roll-outs and availability of gw/nodes & modules etc. so which band is best may depend on where you are located and the propensity for one band over the other. perhaps @Maj can advise based on your specific location and others in the comunity can then help you get your GW online 
Perhaps see GitHub - TheThingsNetwork/gateway-conf: The Things Network Master Gateway Configurations though it’s a little unclear why there are AS1 and AS2 files.
In approximate theory, you’d want to combine the frequency determining parts of the TTN file with the LUT parts of the RAK file. And you’d want to make sure that the “clksrc” and “tx_enable” lines for the two radios match the RAK file, so that they match the actual wiring of the PCB.
Thanks for the replies. The link to the github page with the .json files was what I was missing. I have it working now.
IMHO it would be helpful if TTN could document the server URLs for each band and each country - preferrably in the console web page. This information seems distributed. I have set my gateway to as923.thethings.meshed.com.au - it that correct?