The best way to complete them is at South Raid, in Oramond.
Here:
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During the Raid there is a good amount of walkers :)
If you're a high level EK, it can be easy to go solo in this raid.
But if you're a mage I'd recommend you to be a bit more careful :|
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There also may be some of them respawning here, on the yellow circles (this is not a fixed respawn of walkers, is more like a walker raid):
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And also 1-3 at Oramond Tower, but underground :)