where and how can you get just units for vanilla RTW?

I would really like to have more units for all factions in RTW. Is there anyplace where I can just download a bunch of new units and somehow put it in the game?

There are several unit packs by King Louise Assurbanipal. Check out this one for example of his style. It seems his more recent material is only available at the TWC, though. Try searching their TW modding fora for his projects.