De Bellis Indica is a DBA variant for warfare in India in the 18th and 19th Centuries.
American War of Independence DBA Variant
From Paul Potter, a variant of DBA for the American War of Independence.
Horse and Musket DBA Variant
Here’s a Horse and Musket DBA Variant — primarily for Napoleonic and Seven Years War, but since the basic principles of war in that era covered a huge number of conflicts, you could adjust as needed.
Hordes of the Empire
Hordes of the Empire is a set of free wargames rules for playing 19 century colonial battles. It’s a variant of Hordes of the Things (HotT), which itself is a variant of DBA.