You could also take a look at:
Please note, that a Iaido hakama probably might not be good for aikido-practice since it is sometimes a 'slimmer'.
Another possibility would be to make one yourself if you can find a fabric of your liking. You can buy a pattern from
and somewhere on this site you can find a few tips of how to alter the pattern to make it perfect for Aikido-purpose.
Hope this helps.