Rob Kardashian and Blac Chyna are getting the chance to star in a brand new Kardashian sex tape

Rob Kardashian and Blac Chyna are getting the chance to star in a brand new Kardashian sex tape with an earning potential of 7 figures. 

TMZ obtained the letter sent from Hustler honcho, Larry Flynt, to Rob and Blac -- asking them to consider sho

Flynt says Hustler is looking to be a major player in celebrity porn ... and thinks R&B's fan base will benefit all involved.  

He promises they could be looking at earnings of a million dollars or more. 

Remember ... Ray J and Kim are STILL cashing checks from their 2007 sex tape ... maybe the family business ain't so bad.