I've got a Mew from an undocumented Gen 1 event in Denmark. It was distributed through a Mew Machine at various locations, and I got mine from Bilka (a chain of supermarkets) in Odense. I had an adult (employee or just a guy there, can't remember) help me make space in my party for it. OT is, similarly to the Mew in the post above, DENMARK. I also got a certificate of authenticity, I THINK it was in Danish but it's long gone and I don't remember fully.
I don't have any way to dump GB saves atm, but I've got a GB01 cart reader coming in the mail so I can properly archive, upload, and document the Pokemon, I'm just hoping that my Pokemon Blue save doesn't fizzle out before that happens. I think me and my sis ended up leveling it up to Lv100, though.