I've done a stack of research and enquiries into this, but I'll try and give a brief summary.
Nicotine is a Scheduled poison in Australia. Schedule 7 to be exact. The original intent of this listing is for pure nicotine which is extremely deadly (1000mg/ml, 2 drops can kill). It is the current viewpoint of our health authorities that
ejuice with nicotine for recreational use falls under this listing. Although there are no laws at a Federal/Customs level preventing it's importation, there are laws at a State level making possession and use illegal.
But nicotine can fall under other Schedules depending on it's usage. This is where it gets tricky.
Schedule 6 (like Eucalyptus oil) is when concentrations are at or below 3% (30mg/ml) and for vetinary purposes.
Schedule 4 is for "aid in withdrawl from tobacco smoking" as gum, lozenges or spray.
Schedule 2 is for "aid in withdrawl from tobacco smoking" via inhalation.
Ironically tobacco packed for smoking is exempt (they will claim this is due to State and Federal laws on cigarette manufacturing and sale) and smokeless tobacco isn't mentioned at all, yet can be imported if you are willing to take the risk of getting hit with $400+ in tobacco excise.
The last committee meeting decided that the Schedule 2 listing was intended for the Nicorette Inhaler, and since research shows this is majority absorped by the mouth area, it should be moved to S4 and the S2 listing should be scrapped.
They also decided that eJuice with nicotine for therapeutic use should be considered S4. This is where it gets REALLY tricky.
Schedule 4 requires a doctors prescription. This means (in theory) if you get a script from your GP you should be able to legally import and use eJuice with nicotine. Unless it's majority absorbed by the oromuscal, then it's exempt (no prescription required). Their is evidence that this is how e-cigs work, but since the patient says lung inhalation, that's how they claim it works. This means you should be able to import using the Personal Import Scheme (access to unapproved medicine or therapeutic goods) at a maxium of 3 months use per order or 15 months use over 12 months of orders. This is the LEGAL stance. This is covered by the Therapeutic Goods Act 1990.
POLICY is a whole different matter. The State Health Departments and the Therapeutic Goods Adminsitration claim to follow the advise of the Scheduling Secreatariat and committee decisions, but all refuse to acknowledge that ecigs can be used as a therapeutic product. They CLAIM that it's all Schedule 7 and therefore illegal.
Personally, I think it's a case of nobody willing to stick their neck out and be the one who said "yes you can import it".
Slightly off topic, the TGA claims that e-cigs can't be therapeutic since they aren't on the Australian Therapeutic Goods Registry. But if they were, they could be sold locally and wouldn't require the Personal Import Scheme. They also say you can import Nicorette Nasal Spray despite this not being on the Register since it's an "approved NRT". Yet nobody can explain to be how a product can be approved when not on the Registry - as they take the exact opposite stance on e-cigs.
Finally, they claim you can't import an unbranded solution that is nearly chemically identical to nicotine spray, even if used for the same purpose. That's interesting, as nicotine spray and eJuice are *almost* the same thing. Nicotine spray just has a few extra chemicals not present in eJuice, but the base is exactly the same (PG, VG, nicotine and flavoring).
TL - DR version:
There doesn't appear to be any laws restriction importation of eJuice with nicotine as long as you get a doctor's prescription. Don't bother actually asking any government department about it though as:
a) they don't know their own laws
b) they only tell you half the story and deny the other half (despite links to laws on their own website)
c) nobody wants to stick their neck out