I'm not entirely sure if you CAN find them, if so then they are extermely rare, so you might have to use console commands.

/admin
/spawnnpc su_gem amethyst
/spawnnpc su_gem bismuth
/spawnnpc su_gem garnet
/spawnnpc su_gem jasper
/spawnnpc su_gem lapislazuli
/spawnnpc su_gem pearl
/spawnnpc su_gem peridot
/spawnnpc su_gem rosequartz
/spawnnpc su_gem ruby
/spawnnpc su_gem sapphire
/admin

thanks!

Hey buddy, they don't work. did you give me the right commands?