Some are free, some are not.
http://www.google.com/search?hl=en&source=hp&q=3d+model+soldier&aq=f&aqi=g1g-m1&aql=&oq=&gs_rfai=Cq63y8BtXTMi-Jo_KMsewiMYCAAAAqgQFT9DXxiE
Almost none of them will be Unity ready, most of the ones I found were .3ds format. You will need to import them into something like Blender, then export in a Unity-friendly format.
