Question: If there was no Beatles, where did the toy yellow submarine come from?
Answer: It is just a toy submarine molded or repainted in yellow. Only the 'stalker' fans know the reference to the Beatles song.
Answer: I think it was so those 2 people that knew of the Beatles could prove they knew the Beatles song, since presumably that was a song Jack forgot about.
Answer: None of these answers explain why it's shaped the same as the submarine from "yellow submarine." It's a specific shape that didn't exist before the Beatles, so shouldn't exist.
Answer: Believe it or not, the Beatles did not invent the idea that a submarine could be yellow, and yellow toy submarines were sold for children to play with.