After doing a lot of research, I came across this picture (I don't remember the source at this point) and realized that the juni-hitoe of Heian period Japan was my salvation.
Better still, I found that Reconstructing History had patterns to make the whole outfit! I made the mistake of not using natural fibers for the first attempt and immediately regretted it.
But Jay and I had the opportunity to go to Taiwan for his cousin's wedding several years ago and here is attempt #2 done in some of the luscious silk brocade that I picked up for (I kid you not!) $7 USD a yard! The Yong Le market is a fabric nirvana. I ended up bring back 84 yards of silk brocade (and had to buy another suitcase to get it all home)
The finished outfit (with Ziyi photobombing the picture)
Fabrics: all 100% silk
Level of historical accuracy: Nominal. I was going more for the feeling of the art in the game books and CCG cards that pure historical accuracy.
Shape and lines of of the kosode (under robe) the nagabakama (pants) and the uchigi (robe) are accurate. I've read some research that suggests that the authentic fabric would be a lighter weight silk, more like organza (since the uchigi were layered on top of each other to as many as 12 worn at a time. (juni-hitoe leterally means twelve layer robe). And the L5R game has very specific colours assigned to each family, so I was pretty much stuck with turquoise and white.
I have a second uchigi cut out to use the other side of the fabric (gold with a turquoise design) that I planned to use as an under robe. But we stopped enjoying the campaign and fell out of playing, so I never got it finished.