Here's the skinny on the various different "Star Wars The Force Awakens" previews card sets. There are now four distinct versions of the (same) 8 cards that make up the different sets. These were originally made early this year as virtual cards only as a special way of revealing the names of the characters seen on them for a feature in "Entertainment Weekly" magazine.

1) The first version (and thus the first TFA cards ever issued) was released in two parts. A partial set of 4 were found within some cases of ESB illustrated, but not all. One seller told me he bought 4 cases of ESB Illustrated, but only one of the cases had any of them in it. Luckily for him, it had four sets of the 4 cards.
The other 4 in this initial full set of 8 were distributed one card per issue at the San Diego Comic Con in July. They were found one per issue of the bagged "Lando #1" Marvel Custom comic book (along with a single Luke Skywalker Promo for "Journey to Force Awakens, the same one of those in every issue, and that seems to be the only way that card was distributed thus far). This first set of 8 were issued on "Heritage" card stock.

++++++++The 8 Card set has since been re-issued 3 more times over this last month or so.+++++++

2) Four of the Cards were found in "Chrome Jedi Vs. Sith", (about one per case). The other four were in "Revenge of the Sith 3D Widevision". They seem to be 1 per 4 sets in ROTS 3D, so a total of 125 of each card in those. These are on regular smooth, low gloss or "matte" paper stock (not Heritage which has a bit a rough surface).

3) The full 8 card set with a Chromium/chrome finish in "Chrome Jedi Vs. Sith". These were one per box. Like the harder to find set above, they were unannounced bonuses.

4) Issued just today, there is another set of all 8 given out at the Disney Store. I'm not sure of the card stock used on this set, but these ones are easily distinguishable by the yellow "Disney Store Exclusive" notation on the front of each. These were issued, one at a time, apparently with a purchase, or else to kids completing an "activity", or to those who correctly answered trivia.

So basically, this is a now a 32 card set with 4 distinct versions of each of the 8 cards. Since the new cards (even the retail version that was supposed to come out today) have been apparently delayed, these at least, are something from the new movie than can be collected now. Good luck to those who do!

Wow. Thanks for the update. We haven't seen this many promos since Episode 1.
Does anybody have one so we'll know what card stock is used?

The actual set is scheduled to arrive sometime in December I believe. By that time there will be enough variations of these same promos, plus very likely new promos, to make a whole other set.