Rice paste

I've never used rice paste myself but I think it's something you just test and play around with to get it right. boil down the rice made in a regular way and the goopy stuff at the bottom of the pot would be your glue. I just use all purpose glue or wood glue for most of my customizing. (if you have ever left rice in the pot for too long, you know how hard it is to scrub out the residue, there ya go)

for hishigami you can use any paper that folds easily including standard copy paper. rice paper is available at most art supply stores and is probably less expensive than if you bought it from a Japanese sword supply site. I think Thomas L Buck said he has used newspaper. some people use card stock so they don't have to do any folding.
construction paper could be used and might be extra useful for matching the color of your ito, you would just have to make less folds initially because it's thicker.
adjust the amount of times you fold the strips depending on how thick the paper you are using is. you want the hishigami to be strong but still flexible.

that's it man, it's all about practice hope you will share pics when you're done

Oh, and the ito doesn't need dyeing, so I needn't have stressed on that. It is much darker and richer than in the pics. A little slim, but a nice green.

Called Swordnarmory today. In less than two minutes he got started on sending me the paperwork to return it for free for a replacement. Top flight, I love it.