Need help finding drivers for builds

Possibly a BLF 17 zener driver might work for you
https://oshpark.com/shared_projects/d7oYStVQ

Or the BLF17DD zener
https://oshpark.com/shared_projects/bXpxvUdO

Not really single mode, but they should handle stacked 16340’s

They can be found here

They do sell 16650 Li Ion batts