The instant noodles are discovered as part of the later invention arc, and a source listing on Apple TV identifies the noodles being on sale by Season 1, Episode 146.

What that means

  • The show is a long-running series, so the “discovery” happens deep into the season rather than early on.
  • A Netflix description confirms the series is about Fukuko helping Mampei invent instant noodles, which matches that late-season development.

Quick answer

If you mean the episode where the instant noodles finally become a real product, it’s Episode 146.

TL;DR: Episode 146 is the key milestone for the instant noodles appearing on sale.