There was a d20 product that came out in '03 called "Moonshot." I believe I got my pdf copy from rpgnow, but it looks like they no longer carry it.
I had hoped to use it for a future campaign, but never got around to it. I haven't read much of it, but with a cursory glance, it looks pretty detailed. Here's the Table of Contents:
[sblock=Contents]
Introduction: Selenautica 6
AUTHOR’S PREFACE 6
VOYAGE TO THE MOON 6
NOTE ON THE NAME OF THE MOON 6
LUNAR LORE 6
Names for months on the World of Mystery 6
Ancient stories about the inhabited Moon 9
TICKET TO THE MOON 9
Skyships 9
Stowaway, Kidnapped or Accident 10
Teleportals: The Dancing Giants 10
Thought Projection, Astral Travel and Spells 10
From The Earth To The Moon 11
STARTING OUT 11
Rovac Kirbuck 11
HOW DO THE ADVENTURERS GET INVOLVED? 12
The Rovac adventures 12
The items 12
Other complications 13
MYSTERIOUS BENEFACTORS AND ENEMIES 13
AGENTS OF THE REALMS 13
RELIGIOUS MANIACS 13
COMPETITORS 14
How is Ravoc planning on getting to the moon? 14
Rovac’s Moon Voyager X-Ship (Icosahedron) 14
Rovac’s Skin of the Selenaut 15
Moon Nearside Map (unkeyed) 16
Moon Nearside Map (keyed) 17
Mithra Geography Primer 18
ATMOSPHERE 18
“The Slow Death” 18
BREAKING THE SHACKLES 19
CRATERS 19
DUST SEAS 19
GRAVITY 19
TEMPERATURES ON THE MOON 20
Crateropolis Map (unkeyed) 21
Crateropolis Map (keyed) 22
Mithran Cities 23
CRATEROPOLIS 24
PORT RATING 24
SUMMARY 25
GOVERNMENT 25
CITY FEATURES 25
Crater Wall 25
Factories 25
Gaol 26
Hilltop Citadel of the Science Council 26
Mono-Rails 26
Reservoir 26
Residences 26
Shroom Farm 26
Stables and Docks 27
Temple Island 27
Waste Treatment Plant 27
Mithran Items, Weapons, Armour and Artefacts 28
ARMOUR OF THE ASTRONAUT 28
LUNARIAN DUSTBLASTERS 28
MITHRAN ENERGY WEAPONS 29
MOONSHIPS 30
MOONSKIMMERS 30
Mithra Hazards and Obstacles 31
LUNAR SPELUNKING AND ROCK BREAKING 31
METEOR STRIKES 32
MOONWATER 32
SHEER-SIDED CRATERS 35
SLIME CRATERS 35
Crater Slime (CR 4) 35
WHIRLY-WHIRLY (DUST WHIRLPOOLS) 35
ORGANIC HAZARDS 36
Arillon Fungus (CR 0) / Moonstorms (CR variable) 36
Bayonetweed (CR 1) 36
Beercheese Fungus (CR 1) 36
Bladderweed (CR 2) 37
Brain Coral (CR 4) 37
Candela Fungus (CR 0) 37
Crystal Coral (CR 0) 37
Moon Motes (CR 6) 38
Phages (CR variable) 38
Amzandi Fever (CR 1) 38
Blue Death (CR 3) 38
Drugorth’s Distemper (CR 2) 38
Metalvirus (CR 3) 39
Mithra Monsters 40
MITHRA MONSTERS BY CHALLENGE RATING 40
Anorthostrosity (Archaeoselenodon aka Genesis Beast) 40
Bakthor (Amanaticulus Communatrox Robustus) 41
Charagoon (Selenichthys Oleodontidae) 42
Crater Cat (Felis Gracilis Selenia) 43
Crater Mummy 44
Crater Tiger (Felis Horribilis Dianae) 45
Darul (Umbrapenopteryx Cheryops) 46
Dreth Grazer (Cryptocoelentura Osicranius Cavenum) 47
Dust Ghoul 48
Dust Shark 50
Half-Mithran (Homo Selenis Superior sp) (Template) 50
KREEP (Archaeonebularis Dispersis) 52
Lunar Beast (Template) 53
Lunar Centaur (Paracentaurus Ioiuscis Hexopod) 54
Lunarians (Holoanthropus Artemisia) 55
Mind Lord (Oedicrananthropus Archaeomethis) 57
Mithran (Homo Selenis Superior) 58
Mooncalf (Hymenoptera Neotenendi Spathadontidae) 60
Moon Giant (Gigantanthropithecus Multibrachiae Selenis) 63
Moon Ogre (Troglodytus Spelunaris Selenis) 64
Moon Merrow (Troglodytus Maris Selenis) 65
Moon Roc (Gigantoselenornis Superbus sp.) 66
Selenite (Hymenoptera Dianae) 67
Skeletonoid (Parahomonoida Ferox) 68
Solar Vampire (Template) 69
Steel Spider (Oryxeon Ferropodidae) 71
Mithra Negative Feats 73
Negative Feats 73
Aesthetic Tendencies (-) 73
Inflammable (-) 73
Irrational (-) 73
Susceptibilities (-) 73
Mithra Skills 74
Exotic Weaponry: Crystal-Powered Weapons 74
Exotic Weaponry: Dustblasters 74
Language: Moontongue 74
Lunar Lore (1 slot, wizard, Charisma) 74
Lunar Survival (1 slot, warrior, Intelligence) 74
Mental Defence (1 slot, rogue, Constitution) 74
Pilot, Moonskimmer (1 slot, rogue, Wisdom) 74
Pilot, Moonship (1 slot, rogue, Wisdom) 74
Jumping the (Dust) Shark: Refereeing Mithra 75
Ready Reference 77
[/sblock]
I've tried to Google the product, but I can't find anybody that is currently selling it. The publisher is "Pisces All Media." It sounds like something you might be able to use.