No idea where you would find lowering springs but I think the aftermarket already has coilovers for the new civics.
Or do you want lowering springs only?
H&R Springs was supposed to be coming out with a set, but even up till now they don't list the 2016 Civic, so we'll have to keep on waiting. All they list for 2016 is the Odyssey (i didn't expect that) and Accord.
What does help is looking brands that have produced springs for the 9th gen, good chance most of them will be back for the 10th, and aside from what was mentioned, these are some other brands to look out for:
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