Aside from all the supplements you tried (how long did you give each one to take affect?), what is his general diet? Any alfalfa? What type of grain?
Some of the supplements can have negative effects, depending on his diet already (how much magnesium does he get, etc.). Raspberry leaves is a good natural way to help with calming, without the side affects. We get human grade in bulk (and Chaste Tree Berry powder for our mare).
My Kiger gets rather rambunctious if I feed him alfalfa at all, so he doesn’t get that. Grazing forage, high quality grass hay, raspberry leaves (half a handful a day), LMF Showtime grain (and some additional lysine) is all he gets, and he stays pretty calm.
"Ride fearlessly, but think carefully"