If you're in it for the long haul you will eventually obtain this achievement by normally playing through all 5 character's campaign. If you don't have it by the end and you favor "block" instead, you can rack-up evades in a few ways:
1. Single-out a Giant and evade it's 1-2 punch... it's very predictable but could be time consuming, and dangerous if you are not very good at dodging.
2. Find an Archer group all firing at the same time and dodge all of their arrows at the same time, can also be a bit dangerous... if you miss they all hit.
3. Find a huge group of Wind / Ice Birds and just roll-around in circles dodging, if you get hit it's low damage, and in a large enough group can be done quickly.
Just remember not to die, I'm not 100% sure but if reloading a checkpoint reverts kill count, ect. then it most likely resets evades / blocks as well.