heya, i am an avid prostanthera fan. i had many in a previous garden and am slowly building up my collection at our new place. What are you looking for? if you can wait, i can provide you with cuttings of P. rylstonii (yes go google that one, not a great deal of info!!) i also have P.lasianthos in it's original form. And the usual P.incisa and P. rotundifolia.
At the moment there are some prostanthera's for sale on ebay, aspalathoides and striatifolia.
And finally, while you're at ebay put in a search for "the cradle of incense" by George Althofer. He used to live near wellington in centralwest NSW and 'wrote the book' on prostanthera.
PM me if you want to talk prostanthera.