There is a guy in Austrailia that sells parts for HD 45's on EBay, I bought a front head from him late last year. Shipping was steep but it was perfect. If I can find him I will post his contact information for you. Seems to be a lot of old war time harley bikes and parts in Austrailia.
Most of the parts you will need will come from the USA so shipping will be the killer. Also, you will find like with any vintage motor vehicle (with some exceptions) it will cost 2X to 3X more than its worth to build up from Reproduction parts.
You will be much better off buying a somewhat complete bike needing restoration or a basket case. But, buy all the books aand manuals and literature you can get and do your research first so you know what you are buying. If you buy a bike or part that has been modified or repaired poorly you may end up with junk that you cannot use or spending $$$ to restore it. Nice 45 frames are very hard to come by. Most have been cracked and repaired, raked, mounts removed, bentor cut up somehow. Trying to repair a damaged frame can be costly and you wont know if it;s right until you try to re-assemble everything. Also the VIN is onthe motor casing not the frame so any motor you buy should come with a title or some documented proof of ownership since that is your vehicle identification. I don't know what the laws are in NZ but in theUSA it can be very difficult to register a bike without the proper proof of ownership.
Trythe following EBay Stores:
CastleLandParts
Bulwinkles Place
AAOK
HawgCity1
Throttlemasters
And the following websites:
www.45Partsdepot.com
www.45RestorationCompany.com
45Restoration Company is a V-Twin Dealer and discounts the parts.
V-Twin does not sell retail, only to Dealers so you need to but their parts through a V-Twin Dealer only.
Good Luck
Greg