For anyone after a Ditto one of the new research tasks to coincide with the Detective Pikachu movie is giving Ditto as a reward. It's the "Detective Pikachu: Catch 10 Jigglypuff, Aipom, or Snubbull" one.
Always looking for a trade. Heading to the city tomorrow and doing a shitload of lapras raids. Unfortunely I have tee'd up another lucky friend on the day. Next time Im heading that way will let you know.