Re: "Add-on American Civil War Field-Command and Casualty Figures"
Actually this idea has the potential to be a stand-alone success like the original ACW Command sets were/are.
Just to have heaps more casualty figures, I would buy a truck load of both Union and Confederate Add-on sets. If you put them in a nice box and label them appropriately as "Add-on American Civil War Field-Command and Casualty Figures", your Wargaming customers would buy these to add to their Field Officers and Bannermen. Having more Field Officers and Bannermen just might encourage them to buy more Marching and Advancing Sets, too. And I'd buy them especially for the Casualties.
Why not package them in a nice Box with cool Box Art and encourage everyone alike to buy them even for their existing armies. It could be a good way to attract new collectors to upgrade their existing collections in addition to us. In fact, you would likely be attracting new customers to buy these specialty Add-on Sets for years to come, just like your first Commander sets!
And do the same for the Highlanders and British Armies labeling them appropriately for their contents since their have a little different mix.