It may not be exactly what you are after, but Matt Colville's Kingdoms and Warfare might be worth a look. It is designed to add a warfare mechanic to 5d D&D, but could probably be adapted to other RPG's. It's not really a tabletop wargame.
If you really want to try a tabletop wargame One Page Rules has Age of Fantasy Regiments. The rules a free and easy to learn.
Hope this helps.