Feral it's my opinion you will not get a SRAM 3 speed hub in Adelaide. I'm guessing your talking about a SRAM duel drive hub is that correct the one where a rear cassette is fitted? If my info is correct SRAM have stopped making them and I doubt you will find one in a hurry in Australia. Most bike shops have no clue what you are talking about with Duel Drive hubs and you owning a trike I also guess it has rear disk brakes and the SRAM Duel drive disk version is even harder to get. To purchase one in Adelaide Australia you will not get much change from $600.00 and being so close to Christmas you would be lucky to get it fitted at a bike shop let alone ordered in before next year.
If you have one in your hot little hand I would be happy to fit and lace the rim for you (free of course) to ensure your travels are not interrupted but I'm sorry to say you are not going to find one in Adelaide or Australia.
One other thing is the shifters and click box don't come with the HUb and need to be purchased as a separate item and you won't find a click box here in Australia.
If I can make a suggestion which would be about a 2 week wait for delivery plus a costly one is the link below. Fire them an email and see if they can help with your needs as you might not need the complete kit they offer and they do custom order/build.
http://www.utahtrikes.com/PRODINFO-SRAM ... l_Kit.html
http://www.utahtrikes.com/CAT-Internal%20Hubs.html
That's the best I can offer unless you give some more info about your trike set-up and specs/needs
Ricky