I found this online: http://openlibrary.org/works/OL7655475W/Japanese_costume
It's a multi-format digitized version of an old, public-domain English-language work on traditional Japanese clothing. While it's geared more towards the recent (in the author's time) clothing, it also includes notes on traditional court clothing. (I never knew that a man's court sword was called a "tachi" until now...)
And, hey, it's a free download. I thought you guys might be interested.
The author apparently also did a similar tome on Japanese textiles- along with some other works along the "traditional Japanese arts" vein- but I can't seem to find a digitized copy online...