Following Wikipedia's Garl Glittergold publication history, I perused Deities and Demigods (1980) and the Dragon #61 (1982) article "The Gnomish Point of View" (28-30) for AD&D, Monster Mythology (1992) and Demihuman Deities (1998) for AD&D2E, Deities and Demigods (2002) and Faiths and Pantheons (2002) for D&D3E, and Complete Divine (2004) for D&D3.5. This is in addition to a handful of other sources. You needn't've worried about being overwhelmed; there ain't much.
Garl Glittergold's battleaxe Arumdina
The Encyclopedia Magica (1999) for AD&D2E lists Garl Glittergold's traditional weapon in Axes under Arumdina (112) and Garl Glittergold's Battle (118). In both entries Arumdina is given statistics to indicate that it's "a unique and potent item (often called an artifact or relic)" and that it "is so priceless that it is impossible to rate its true barter value."
Although Deities and Demigods for Dungeons and Dragons, Third Edition downgrades Arumdina to a nonitelligent (yet still epic) +5 dancing ghost touch speed battleaxe, Arumdina is said by multiple sources to be intelligent as well as capable of cleaving through stone as easily as air and, in most cases, once per day of fully healing the god of any damage that's been dealt him.
Here're some things to consider if you want to homebrew your own.
- Monster Mythology says that Garl Glittergold embarrassed Grankhul, hunter god of the bugbears, by masquerading as a deer. A quest for Garl Glittergold's sacred deerskin cloak or something isn't bad.
- Faiths and Patheons says that Garl Glittergold has "the largest collection of jokes in the multiverse" (135). A copy of his jokebook would certainly be an entertaining basis for an artifact.
- Complete Divine's gem of the glitterdepth (97) increases a devoted Garl Glittergold worshiper's Wisdom and gives him a sense of his surroundings while spelunking, alerting him to the location of floors, walls, and ceilings.
- Complete Divine mentions offhandedly as a quest for Garl Glittergold worshipers "seeking the long-lost Ebondark Gem Mine on the Elemental Plane of Earth" (112). A map to it or the gems themselves could be artifacts.
- Magic Item Compendium's hooked hammer of the hearthfire (52-3) is a combination hammer and pick that, when wielded by a devoted worshiper of Garl Glittergold, bursts into flames that damage those that are struck by it.