The query here is in relation to the supply of the medicinal supplies, not in the actual treatment of the condition.
It'd certainly be no harm to chat to a GP about such a trip, but the Diabetes Care team is certainly the best point of contact on the actual supply when in Oz (or anywhere outside of Ireland). The LTI (long term illness) scheme we use possibly won't cover you (I've never looked into this so it might be possible to avail of free supplies in foreign countries) so any supplies might have to be paid for from your own pocket (and insulin certainly isn't cheap!).
The comment about "you can only get a 3 month supply at any one time here"? I've never come across this before. Any one pharmacy might have issues with giving out too large a supply to one customer (another diabetic might be left short as a result), but I've never heard of any restriction like this. Each prescription is usually for a period of around 6 months (I always just assumed this was timed to fit in with the next diabetic check up), but on that prescription there is no limit on how many times it can be filled (or at least none that I am aware of). In a worst case, I'm sure the doctor could detail multiple filling of a one off prescription to allow for travelling (you may have to call to a few different pharmacies to avoid clearing one out, or else contact them in advance to warn of a higher than normal request).
Having said all that, 7 months travelling is a long time to hold onto supplies. The link above on travelling states a 2 month shelf life for insulin out of a fridge and far longer in one, but I'm not sure if I'd be confident with 6 month old supplies which have been travelling through hot countries. This is a scenario your Diabetic team will have come across before, so I'm sure they'll have no problems helping you to the best solution.
As a T1 IDD I'd be interested to hear any advice they do give. I've never gone travelling for more than a month so it's a problem I've never looked into.