I can find no evidence that #6 & 7 of this series were ever published (GCD, ComicChrom, CCL, etc.)
It’s possible 6&7 were solicited, but not put out as such…perhaps the contents were re-purposed into the follow-on 5 issue series Extinction Parade: War? I’m not sure, but it appears that the Extinction Parade 2013-14 series was only 5 issues.