Just a gun bit of info for others, you can find Pichu in Viridian Forest and Cleffa in Mt.Moon if you're lucky. Those aren't on the "Encounter" list for those areas.
Also, Big brained strat. You could have all three starter pokemon, you just need to transfer all of them using the transfer box in storage system.
After testing: Yup! Totally possible. Now I got all three starters! Why choose when you can have all three?!