Hello, F2,
If you fail to come up with the correct straps, your only option would be to fit strap inserts into your board. Personally, I prefer having this work done by a professional, say a surfboard manufacturer/repairer, but you may be able to do it yourself. Here are some links:
http://www.chinooksailing.com/products/index.php?cPath=64&sort=5a&page=3Your local windsurf shop should be able to source the inserts from Stuart Bell in WA who are the Chinook agent for Oz.
boardlady.com/inserts.htmboardlady.com/extrainserts1.htmHope this helps.