there is no single source of a set of miniatures for C&C Ancients. Essentially you have to find and buy miniatures to suit the game / make the armies that you desire.
The very first thing you need to consider is what scale miniatures (cause I'm assuming you want them to be the same scale). Generally speaking to fit into the board hexes you are looking at 28mm or less, but you probably also need to think about how much you want to spend on miniatures. They aren't cheap.
You can of course bling the game totally, with a mat, bigger hexes, terrain and minitures of any scale you choose.
I liked 20mm (1:72nd) scale, and there is a good resource called Plastic Soldier Review
www.plasticsoldierreview.com/Index.aspx
15mm is a very common scale, with many suppliers, and usually metal.
and then there is the painting..
