OK, I know this was a post from awhile ago, but I have been trying to find an answer, and to be honest I still don't have one, but I am closer.
So far Pre-3 kingdoms (for reference purposes the spelling is Wade-Giles)
The references are few but boxing was mentioned in the following
Chou dynasty (1122-221 BC) – The Book of Rites
The spring and Autumn Annals (772 – 481 BC)
Literature from the warring states period (403 – 221 BC)
All mentioned archery, fencing, wrestling and boxing.
The wrestling was a rough form featuring butting and other unsophisticated tactics.
This is characterized in a primitive form of fighting called ChÂ’ih yu-his, which stemmed from the fight of the legendary Yellow Emperor Huang Ti and a horned monster called ChÂ’ih Yu, four thousand years ago. This is not as mythical as it sounds, there was a sport preformed by farmers where participants put on cow horns and butted each other in Ancient China.
Jump forward to The Han Dynasty (25 – 220 AD) a famous surgeon Hua To developed a series of exercises based in the movements of 5 animal; tiger, deer, bear, monkey and bird, which is still used in various boxing schools.
I also believe it was around this same time that Buddhism came to China and the 4 elements composing the body were introduced, earth water fire and wind. These have been used to develop the internal systems.
[Asian Martial Arts – Donn F. Draeger and Robert W. Smith]
So far I have not been able to find any reference to Martial arts during the three kingdoms period. The next reference I find jumps to the Tang Dynasty to the Shaolin School.
I'm still looking.