Hi Grace, another member from the city of Churches. I spent my teenage years in Ceduna, not that far south of you.
Welcome to the site.
Finding what to sell is one of the hardest parts to be honest, it can cause quite a lot of frustration just getting that far, let alone trying to be successful at it.
Best advice I could offer is to not panic, I know you are working to a time frame, but if you panic about it you will most likely end up going around in circles and not getting very far at all.
You must have plenty of craft type markets scattered throughout Adelaide, so why not just go for a weekend walk around, take a look at some items and talk to some sellers, never know, you may just find something unique right under your nose.
Going to a few garage sales could also be good for finding some products of interest, and if you can talk a good deal then you can also buy CHEAP!
I guess at this point it's more about finding product that you would be interested in selling, so the more places you stick your nose, the more product possibilities you'll find.
Don't fall into to trap of trying to source everything online, use your location to its full potential, that's where you have the best chance of finding products to sell that no one else has.