Ninecircles.com has an
obi that's 7cm by 480cm. That's... (quick math)... ~2.75 inches by ~15.75 feet. That's kinda skinny but should still work for iaido. The
belt I have is about ~13 feet long, but that may not be long enough. They have an
elasticized belt, which is also ~13 feet, but may work for you. Another option may be their
velcro belt. I'm not sure how long that one is, but you could email and ask.
I know you can find some of these belts at US stores, but I know the guys that run Ninecircles, and I know they'll try and help you out.