well, actually in the new fluff, sometimes necron phase technology doesnt work as well as they want it too, and sometimes stuff gets left behind. So its perfectly find to model some necron stuff badly damaged as basing material.
Other than that, it would be cool to see a cron trying to put itself together, only to be stepped on by something (a talos, or a warrior shooting it) and then you can always use scarabs. They are a dime a dozen
Also GW just put out different basing kits, and if i remember right, one of them is almost perfect for a cron world (I forget which though). So there are a ton of options out there for you now.
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