I'll give you half an answer. The correct material to use is Kakucho Sageo...if you go on eBay and search on those words, you will find a guy in Japan who sells them in 180cm lengths. You want to select the colour Gold.
A while back in this thread, there was a diagram that showed how to tie the sailor knot that runs about half the length of the strap:
http://www.therpf.com/f24/sucker-punch-costume-thread-92563/index24.html#post1628990
Also take note on how long this sailor knot runs...it is not the entire length of the strap.
That's the only answer I can give you so far. I received my Sageo in the mail yesterday. I need to figure out how to tie it, and whether or not 180cm is long enough. I think that I can easily figure out the sailor knot, but maybe not the attachment to the scabbard. I am mostly worried about the length of the strap...can I make the strap from just one Sageo, or do I need to buy another one?
When I figure it out, I will post here.
Parks