What kind of notation is used for kouta?
I’ve got two small books of kouta: one is from 1954 and is in the vertical system generally used for Nagauta, and the other is from 1969 and is in bunkafu notation (also used for Tsugaru shamisen). So I guess it depends on the school.
You might know about Liza Dalby’s book Kouta, which is mostly translations and explanations of 25 songs, but does include shamisen notation for one song (in bunkafu). It’s a good read - informative but casual, definitely worth looking for if you’re interested in the subject.
She’s also made a DVD about kouta called Geisha Blues. I haven’t seen it yet, but I’m sure it’s more than worth the price ($12), especially if you want to learn to play.
Here’s the link:
http://www.uzushop.com/product_p/liza5.htm