Here are some original old school D&D modules that should be easy to find and not cost you an arm or a leg if you buy them online:
I1 The Forbidden City (TSR, 1980): Old school AD&D sandbox setting in a "lost" jungle city inhabited by snakemen (yuan ti), frogmen (bullywugs), and lots of other weird and dangerous creatures. Lots of room for development here and no two adventures will play alike (due to multiple adventure paths and foes).
B4 The Lost City (TSR): This old school original D&D module consists of a pyramid buried in the desert sands which holds various degenerate groups battling each other for control of the underground empire.
X1 Isle of Dread (TSR): Lost island sandbox setting with lots of different adventure ideas
WG4 Lost Temple of Tharizdun (TSR): written by the master himself, EGG, this AD&D adventure takes place in a long abandoned temple to a dark god hidden in a mountain valley. Initial conflict is against monsters who now inhabit the structure, but if the party delves deep enough they will run into Things Best Left Undisturbed.....!
Axe of the Dwarvish Lords (TSR): This AD&D supermodule written in the 90s takes place in an long abandoned Dwarvish citadel now inhabited by an army of goblins.
Gates of Firestorm Peak (TSR): This 90s AD&D module takes place in a weird, otherworldly mountain that has connections to a "Far Realm" of madness and insanity. Sounds like it would fit right in with Raggi's stuff!
Not as easy to acquire are the classic Judges Guild modules Caverns of Thracia and Dark Tower (however, the 3.5 reprints should be a lot easier to find and are backwards compatible). Both are great and concern ancient, underground empires with lots of evil things lurking about.
Many of the Classic Traveller adventure materials could be easily adapted.
easily adaptable:
Adv 8 Prison Planet
Adv 9 Nomads of the World Ocean
Adv 11 Murder on Arcturus Station
Most of Sup 6 76 patrons
CT D02 Double 02a Across The Bright Face/Mission On Mithril - both halves!
CT D04 Double 04a Marooned/Marooned Alone
Some "rather iffy - bends the 'verse" Traveller adventures:
Adv 2: Research Station Gamma - intelligent aliens; otherwise, a rather doable conversion
Adv 7: Broadsword - the adventure itself is suitable, but most of the module isn't the adventure.
Adv 10 Safari Ship - again, more about the ship than the adventure
CT D01 01a Annic Nova/Shadows - both deal with aliens pre-current imperium.
CT D05 Double 05a The Chamax Plague/Horde - Alien life.
Ones that don't fit well
Adv 1: Kinunir - it's a "show off the system mechanics" issue.
Adv 3: Twilight's Peak - intelligent aliens; ancients. Strongly OTU
Adv 4: Leviathan - another "show off the mechanics"
Adv 5: Trillion Credit Squadron - Not an adventure
Adv 6: Expedition to Zhodane - Aliens, specific-to-OTU theme.
Adv 12 Secret of the Ancients- Aliens, specific-to-OTU theme.
Adv 13 Signal GK- Aliens, specific-to-OTU theme.
The Traveller Adventure is chock full of useful stuff, but the campaign metaplot is unusable due to both being too OTU, and involving too many aliens. Many chapters, however, are perfect fits... Zilan Wine comes to mind immediately.
MT didn't have many separately published, tho' many were in Traveller's Digest or in Challenge. Both Knightfall and The Flaming Eye are so OTU focused that conversions would be unrecogniable and lots of work.
Mongoose's Traveller has a few that could be easily adapted... In general, tho' only 760 Patrons really is worth the time.
Best Answer
The Plane Above is the 4E sourcebook for the Astral Sea, and includes a paragon-tier "mini adventure" set in the Astral Sea, as well as other adventure hooks. The book is about 150 pages, and the adventure is only a half dozen of those, give or take. The Manual of the Planes also spends about 30 pp on the Astral Sea, but there are no adventures. I believe there may be some hooks.
There are sourcebooks from previous editions that cover the astral plane, most notably 2E's Planescape's A Guide to the Astral Plane (which does not contain any premade adventures). The cosmology of 4E differs drastically from that of previous editions, however, and the Astral Sea of 4E is quite different from the Astral Plane of the 1-3E "Great Wheel" cosmology.
To the best of my knowledge and research, there are no adventure modules published by Wizards or TSR that were set in the astral anything.