Man ... I'll be spewing then cuz you might as well have got an Aus spec AE86 with the drum rear as there's no difference.
You'll either have to get a custom rear diff with discs (ie. modified Hilux diff) or another Jap spec rear diff with discs to get them.
Either way = more $$$ for you ... that is, if you can find one ...
Looks like the importer ripped you off by pulling the rear diff with discs + LSD and selling it separately ... they cost about $1,200 - 1,600 AUD on average separately.
If you haven't bought it yet, then walk away unless they are giving you a good price for it.