Finding placeholder art can be a pain. Testing your engine animations, or simply making a small prototype or tech demo is not that usefull when you can't use proper models.
To circumvent this issue you can look for free art online, on places like http://opengameart.org, rip from other games, or buy general purpose art packs. This is what we did. To be able to properly test our sprite animation handling, attacking, movement and other things, we purchased the GarageGames 2d Fantasy pack, which contains animations of movement, attacks, and other cool stuff.
The pack cost us 30 usd, which fit well on our small pockets and allowed us to have some solid placeholder art.