Slitherine

How do you find the unit pics to reuse them for different factions? I want to add forces to the French nation, such as American and British Equipment. It should be easier to already use the ones made for the game. What is the easiest way to do this?

The easiest way to get your head around this is to download an existing mod and take a look at the files you need to mod.
The official (small) Battle of Britain is a good and simple example.
All unit stats are held in the Data/Units.csv file. You must duplicate one of the unit rows and give the unit an unique number.
Then add a line in the Language/english_mod files which points to the duplicated unit.
Always make a backup before you edit the units file, one tiny error and the game mod may not start properly.

If you have more questions, please ask the in the Scenario design sub-forum.

Here's an example of adding more French units (from my MicroMod). Note that all unit IDs starting with 10000 are duplicated originals.
I use a really high number since there is little chance of the official unit number reaching that level.