You can acquire these files through the following official channels:
The developers of Vita3K actively warn against using any pre-made BIOS packs. They are outdated and break compatibility. download psvita bios full
Open your emulator, navigate to the Install Firmware File option, and select the .PUP file you just downloaded [2]. You can acquire these files through the following
PSVUPDAT.PUP (Main system firmware).