When it comes to region-exclusive Pokémon in Pokémon Go, reliably finding them can be difficult. Most of them are spread all over the world in specific places. For Blue Striped Basculin, you can only find this version in the Western Hemisphere, which means that if you live somewhere in the eastern part of the world, chances are you won't find this Pokémon. If you can find it, what are your chances of catching a bright blue striped Bascluin?
Although Basculin has been in the game since early 2020, it hasn't received a brilliant version. Both the blue and red striped version do not have an active glossy version, which means that if you are looking for it you will have to wait for a particular event. Each time a new Shining Pokémon is released in Pokémon Go, a bigger event occurs. For example, the Heracross Brilliant Event occurred alongside the 2021 Ultra Unlock Part 2: Space Event, and although Heracross was a regional exclusive, like Basculin, the event expected many of these Pokémon to be available throughout the world.
The same will likely happen for Basuclin, although we doubt we'll have to wait for an Ultra Unlock event. It could happen closer to the end of 2021 with a small event that will give region-exclusive Pokémon a chance to appear for everyone, but we'll have to see. Niantic hasn't provided any confirmation as to when a brilliant version will be released.