just as the title say
Find a Male Crustle (or Dwebble) that already know Stealth Rock. (Lv 24)
Find a Female Foretress.
Breed the Pokemon together, and the offspring should be Pineco with Stealth Rock.
Hope I helped. :)
Sources: Multiple parts of Serebii
Breed a female Pineco/Forretress with a male Dwebble or Crustle. Dwebble learns stealth rock at level 24.
Hope this helps :)