25 million French households * .75 (% of households that don't own) ^ 15 (number of households you are close enough to drink their coffee) = ~334,000 households that neither own nor know owners of this coffee style.

note: I made 15 up, but it's 5.9 million at 5 households and 18k at 25. I'm not French nor really a household but I think the actual number is somewhere between 5 and 25, and the numbers in that range aren't horrible.