Many users have uploaded "Ghostlight" or eShop "Redump" collections to the Internet Archive. Searching for "3DS DLC CIA Collection" often yields results for the entire library.
You must ensure the DLC region matches your base game. If you have the North American version of Stretchmo, you need the USA DLC CIA; otherwise, the game won't recognize the extra levels. Stretchmo 3DS (USA) DLC CIA
To use these files, your 3DS must be running custom firmware like Luma3DS. You typically install them using a tool called FBI . Where to Look (Community Resources) Many users have uploaded "Ghostlight" or eShop "Redump"
Stretchmo (known as Fullblox in Europe) is the fourth game in the popular Pushmo puzzle series developed by Intelligent Systems. Unlike its predecessors, Stretchmo was released as a free download on the Nintendo eShop, giving players a set of introductory puzzles for free. To play the full game, users had to purchase "Attractions" (DLC packs) through an in-game menu. The DLC "CIA" Situation If you have the North American version of
Subreddits like r/3dspiracy have extensive megathreads and guides on how to safely find and install DLC for games that are no longer available for purchase. Safety and Requirements
This is currently the most popular and comprehensive library for 3DS content. They host games, updates, and DLC specifically formatted for easy installation. You can visit the hShop website and search for "Stretchmo" to find the DLC for the USA region.