I've smoked c5 a few times but can't find seeds for it anywhere, has anyone heard of it?

I think you mean C4...
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Chimera Seeds C4;
Explosive! Same mothers as the Frost Bite, but fathered by shiskas! Both lines are huge yielders; the shisk brings down the flowering time and the tasty moms improve upon the flavour and aroma. The trim from these busty ladies makes excellent bubblehash- truly worthwhile. Big big fun!
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