Where do I find the tv channel frequency for a specific postcode so that I can manually enter for set top box

try this:

http://whirlpool.net.au/wiki/digital_channels

I think the Sydney one is out of date, but I am not sure about the rest. I think SBS changed frequencies in the restack.

Just make sure you use the bandwidth as 7mhz if there are options. I had a problem where the system I use couldn't autodetect the bandwidth so it would time out. When I set it to 7mhz, it worked fine.