Actually, if you just need it for the entry, I may have a friends hacked Mew lying around somewhere, so I should be able to trade whenever you are ready
Hey dude, I've actually had a big problem. I put my Mew onto My Pokemon Ranch and lost my Pearl save file, so I've effectively got my Mew stuck on My Pokemon Ranch. But if you maybe wait a bit, I'm working on getting the Cherish Ball Mew from My Pokemon Ranch at the moment, so I can trade it to you for Pokedex entry only, and in return you can just trade me a Pokemon that I need in my Pokedex as well. So effectively, we're helping each other out