I've been looking for a local Aussie supplier at reasonable prices too and I haven't found anyone who a.) carries stock, or b.) has comparable prices with eBay stores and o'seas dealers, except for the Hagon shocks I bought.
I've tried wreckers here and seriously you can buy parts in the US and have them shipped to Aus and save a bundle, you just have to bundle stuff up in one order and be patient. For example I looked at the Kerker site and tried both Australian distributors, one quoted 'over $1100' and the other said he hadn't sold a Kerker in 5 years and wondered why he was still listed as a distributor. I contacted Dynoman and you can land a base Kerker (without add-on perf baffle) for about $720 AUD, even with $123 USD in freight.
As for Ikon shocks check the forum and you'll find they're $655 AUD, but you can buy them ex the US for something like $475 plus freight.
Freight is the thing to watch out for, I canceled an order with Parts'n'More the other day because they wanted $53 USD to ship 4 carb kits and 4 pods to Aus. I bought them from mrssuperdeals, an eBay store.
You've got to do a bit of homework, there's some amazingly good deals out there. On eBay (search "worldwide"), and use some good sites like these:
http://www.cyclexchange.net/index.html Nice carb kit and lots for Choppers, no reply to emails
http://www.dynoman.net/bikepages/sohc/index.html Great response, well liked in the SOHC4 forums
http://www.oldbikebarn.com/ Huge store, quite expensive
http://www.ttr400.com/index.html <-This one is very interesting
http://www.rearsets.info/prices.html Omars, home of XS650 Tracker kits and other fibreglass
http://www.xtreemedecals.com Decals, cheap
http://www.yamiya750e.com/ Lots of Repro kit and Yoshimura copy 4-1 but no online payment system :-(
http://www.z1enterprises.com/catalog.aspx?pid=HP441 Big store
https://www.partsnmore.com/cat_index.php?model=cb750_sohc&category=x Cheap and cheerful store, were very good about canceled order
http://www.benjiescaferacer.com/home.html Beautiful body parts.
http://www.airtech-streamlining.com/hondaz/CB750SOHC1969-77.htm Fantastic priced fiberglass (for the K and F !!)
http://www.bikeboneyard.com/honda1.html <<- Check out the secondhand prices.
Cheers.