The Din of Battle Blog has a nice scenario for a Boxer Rebellion Battle of Yangtsun, as well as an after-action report.
colonials
Bundok and Bayonet Colonial Rules
Bob Cordery’s Bundok and Bayonet free colonial wargames rules are available here. They are a clean, well-written set that use a card activation system. Two things I really like about these rules: 1) that you check morale before moving 2) a bucketsful of dice mechanism for combat.