You need to install on your official 3DS. This unlocks the NAND (internal memory). The process varies depending on your system version, but generally involves a seedminer or kartdlphax method.
The BIOS is copyrighted software owned by Nintendo. Distributing it is illegal in most jurisdictions. Unlike abandonware, the 3DS is still a relatively modern console (its online store closed recently, but the hardware is actively traded). Downloading a BIOS file from a third party is software piracy. Nintendo 3ds Bios File Download
Given the complexity of BIOS dumping, most emulation experts agree: You need to install on your official 3DS