You don't need the installer to get add-ons.
I am not with Laminar Research; just a flight simmer.
You are in the wrong forum asking about not receiving your Steam product key. You need to go back to the reseller or a steam forum. This forum is for those flight simmers who have purchased the genuine X-Plane software from Laminar Research. Have a look at the following link https://questions.x-plane.com/22262/are-there-anyother-ways-launch-plane-other-than-steam-store.
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