Where can I buy large grade Griselinia?

Dont want to wait 5 years for it to reach 2.5 mtrs high and bushy. Can i buy bigger and bushier plants anywhere?

How tall are the ones you've seen? I've seen them for sale in about four different sizes. Biggest at nurseries.

Sure you can, they are pricey though, but you must already realise this. Look out for a wholesale tree company. In Auckland they are companies such as big tree company, blackbridge, theres a few others i cant remember at the moment. There may be one near you. If not contact your closest good garden centre and see if they can buy in /source some for you.

I see you're from Morrinsville. (My old home town for many years) My brother has the hydroponic lettuces at Motumaoho, but we don't communicate any longer. He's too stressful to be around.
But back to business.
Try the nursery just out of Matamata. We bought some very large trees from them, including griselinias when we wanted to screen a view that wasn't very nice.
Having said that, do you particularly want Griselinias, what about feijoas that will grow to the height you need, in no time, and you'll have the added benefit of fruit too.
Bear in mind that if you take my advice on that matter, they send their roots out to goodness knows where. We have next door's roots through under our concrete slab for the van, and then on into the gardens that are handy, and they are probably even under the house.
However, they screen us from storms from the east, and shade in the morning is nice.
Evergreen too of course, as are your griselinias.

Not close to you but we bought some from Palmers Remuera, Auckland. They advertise as only stocking landscape grade plants.
What about contacting someone like Wairere Nursery and seeing if they can source some for you if no luck elsewhere.