Keep it all Honda, man!
ATC200 master cylinder will work, MB5 too, but that's a harder bike to find parts for.
Chinese jobs go for under 20 (plus ship) on ebay, and include a brake light switch. Can't speak for the quality, obviously, but fwiw, I have had good luck with cheap MC's lately. Fit and finish looks decent enough.
I'm using an MB5 unit on my C100- works good enough, certainly better than those nasty cable operated ones.
Hope this helps!