Deep Gnomes

There aren't a lot of sourcebooks or campaigns that heavily feature the svirfneblin, with the exception of the Out of the Abyss 5e adventure module which has an entire Blingdenstone chapter! There is also a playtest 2e adventure module, Reclaiming Blingdenstone (2012). But most Underdark sources have a page or two on deep gnome society or will feature deep gnome NPCs for encounters. I've tried to catalogue everything I could find on them here.

As usual, the most recently released book supplants the information in older editions, so something stated in 2e might be replaced or discarded in 5e. However, I like using the history of the development and check what might have been replaced and whether or not I want to play with it in my own work.

Deep Gnome Cities

There is a table of Underdark Cities on Candlekeep with a column stating the races that inhabit the cities. It also lists the sources these cities come from! The biggest and most well known svirfneblin city is Blingdenstone, which is heavily featured in The Legend of Drizzt's Exile. There is also Vault of the Star Ruby,

Books with deep gnome descriptions:

• Mordenkainen's Tome of Foes 5e (2018)
• Sword Coast Adventurer's Guide 5e (2015)
• Races of Faerun 3e (2003)
• Underdark Adventure Guide 3e (2003)
• PHBR The Complete Book of Gnomes & Halflings 2e (1993)

Other resources I've looked at include the Drizzt novels and various campaigns (Night Below, Out of the Abyss).