From GameWatcher: “Scrap Mechanic’s survival mode introduced hunger and consequently farming to the early access game. For a crop to grow you first need to find its seed and while most are easy to obtain, players have been having trouble locating the fabled pineapple seed, which along with broccoli make up the top tier food group.”
Source: N4G PC Scrap Mechanic Pineapple Seeds – Location and How to Obtain