If it’s only 7-10 days you can spare I’d forget Aus & head straight to NZ.
Wherever you end up in NZ there’s invariably somewhere to ride. Can’t advise you on guides, but head to a local bike shop & the locals will fall over themselves to show you all the best spots.
Weather will be perfect in March time too! If you end up in Rotorua you must ride Rainbow Mountain. Tiny ride but the descent from the top is hilarious (and you can wash your bike in the thermal pools at the bottom).
If you do decide to ride in Aus though, I’d recommend Tasmania, there’s new trails developing all the time out that way (Derby trails well worth a visit).