Magnemite, the magnet Pokémon from Kanto, can be found in the wild in Pokémon Go. Yes, Magnemite can be shiny in Pokémon Go!
Magnezone is a pretty decent electric-type attacker, if set up with Spark and Wild Charge. It does more damage as a Shadow Pokémon (which you can probably already expect). It still falls behind Electivire, so if you have an army of those, you don’t really need to invest in Magnezone.
What is the shiny rate for Magnemite in Pokémon Go?
As per old research by the now-defunct website The Silph Road (via Wayback Machine), the shiny rate for Pokémon on a regular day is approximately one in 500. Magnemite is not a confirmed Pokémon that gets a “permaboost” (meaning that it’s a rare spawn and thus gets a boosted shiny rate).
What can I do to attract more shiny Pokémon?
Not much, unfortunately. It appears to be random chance. Shiny Pokémon catch rates are set by developer Niantic, and they are typically only boosted during special events like Community Days or Safari Zones, or in Legendary Raids. There are no consumable items that boost shiny Pokémon rates.