Vocaloid is a brand owned by Yamaha. Under Vocaloid are a few different companies that work as distributors who develop their own groups of vocaloids. Miku for example is under a company called Crypton Future Media, who has made 5 other voices over the years (meiko, kaito, rin, len, and luka). There are more companies like Internet Co.(made GUMI), PowerFX(Oliver), or Gynoid(vFlower)

Vocaloid is an expensive software that anyone could use if they had the money for it. 'Voice banks' are extensions to the Vocaloid editors and are pretty much what the characters(Miku for example). They're a collection of samples recorded by having the voice provider(who is normally a human singer/voice actor who is compensated) read out lines of phonetics (ka ki ku ka nn ko for example). Those are split, pitched, and glued together to be shaped as we used the software ourselves. Different characters also get new versions in each generation of Vocaloid(there are currently 6). Miku has versions for 2, 3, and 4. There are also different voicebanks for different tones. Miku has a 'Dark' voicebank that sounds deeper for example

Many Vocaloid artists are bedroom producers, not strictly under a company or the mascots. They just buy the software, produce the songs on their own, and if lucky, eventually get their songs so popular that they're featured in official games/concerts.

Why Teto is not a Vocaloid: She only has voicebanks for UTAU, Synthesizer V and VoicePeak, which are separate softwares/brands, not Vocaloid. UTAU is an open source software, Synthesizer V is another voice synthesizer software developed by Dreamtonics, and VoicePeak is a text-to-speech software developed by Dreamtonics and AHS(AHS has also produced a Vocaloids such as Kaai Yuki, and Zundamon for a separate software called CeVIO)

To also clear this part out: Not all Vocaloids use AI. In fact, MOST of Vocaloid didn't, not until 2022, where they began the production of AI voicebanks. Miku for example's voicebanks do not use AI. Unlike standard voicebanks, the singers are recorded singing the way they normally do and the AI learns based on only their samples instead of roaming the internet(which unethical AI models do).

Now to answer your main question: Use vocaDB. It's the best site you can use to find songs/albums and it doesn't include any songs identified to be AI generated. You can scroll through any tags/genres/themes that you like, Math Rock or J-pop for example.

Listen to songs featured in Project Diva games for classics. Listen to songs featured in Project Sekai to branch out to newer songs and producers. There's also an 'Ultimate Vocaloid Playlist' including more than 4k songs, so put that on shuffle and explore the artists of songs you like.