Byron Campbell and Neil Edmonds wrote 'adventure guides' for the base sets, which are exactly the kind of expanded stories you are looking for.
You can find them over at BGG.
Search for your base set, go to files, look for the adventure guide, set up a free account and download them. Note that there is one guide for each complete adventure path, and the guide for Mummies Mask is being written right now.
Then, there are also the great homebrew adventure paths for Rise of the Runelords and Skulls'n'Shackles, written by Ron Lundeen, which you can find on his homepage for free.
Lastly, you can also buy the pdfs of the organized play scenarios for 1$/scenario and just play them at home.
Lastly, you can also buy the pdfs of the organized play scenarios for 1$/scenario and just play them at home.
You can find those PDFs here. The scenarios in the box aren't the same as the ones you were playing at the store. The ones at the store are the organized play scenarios. They give each box a second adventure path. So, if you want, you can find the "season" that goes with the base set you both (i.e. Rise of the Runelords base set = Season of the Runelords, Mummy's Mask = Season of the Plundered Tombs, etc) and then play them.
Hope you enjoy it.
Thanks for the shout-out Doppelschwert!
The location card text is nice, but the scenario cards are definitely lacking. I've only played Rise of the Runelords; but, the worst part is the Adventure Path card descriptions spoil some of the scenarios which use a "Who is behind the great evil" approach. Scenarios 1 & 2 aren't much of a mystery when the Adventure Deck card told me who the ultimate villain was in Scenario 6.
I've gotten all kinds of feedback about the Adventure Guides ranging from "wouldn't change a thing" to "too long" or "would be better with professional writers." Obviously, we can't please everyone; but Byron and I try to do our best. Paizo and Lone Shark aren't going to invest in writing full stories for each base set; but they gave us the Community Use Policy and they share some game art with us, so we can write our own fan stories legally. I'm right there with you wishing for a professional write up. I'd save myself about $80 and 100 hours each box set release.
I always assumed if the Adventure Guide was too long, somebody could create an abbreviated version and release it themselves. It's much easier to remove information than it is to add it. When I wrote Wrath of the Righteous, I had the luxury of using the format Byron set up for the first two guides, so "more of the same" seemed like a good idea, because it's worked really well for JJ Abrams. In fact, If I ever met a Paizo or Lone Shark staffer,
If you check the Rise of the Runelords file section for Boardgame Geek, you'll also find "Meet the Heroes" and a "Blessings Guide." The former provides a more complete backstory for the heroes, while the latter explains who's represented on the Blessing Card you're playing - it makes you appreciate why Kyra wants to collect Sarenrae blessings, besides the fact that her role card tells you to.