I'm not actually sure how rare an Archen is to be honest! There might be other trainers in Johto or in the area across the ocean.

Still, I think a white Eevee is a little more unique than mine! _{[Sorry Julius! He still loves that goofy beaky face of yours!]} I heard they can evolve into a bunch of other Pokemon compared to the one or two that most other Pokemon have, so maybe if you find more white ones you can have all of them as a different color?