Shiny Solrock Pokémon GO can be caught, and the Summer Solstice event is your chance to get your hands on one.
The Summer Solstice event will feature increased spawns for Solrock and Lunatone, and will put them in regions where they normally aren't available. Solrock only appears in the western hemisphere, but the event will let you catch one anywhere in the world. After the event, Solrock will move to the eastern hemisphere.
Shiny Solrock Pokémon GO: How to Catch
The event most likely won't feature an increased spawn for Shiny Solrock like a Community Day might. You're still fighting the normal Shiny rate of one in 450. You'll just be encountering more of that Pokémon, giving you more chances to roll the dice.
Shiny Pokémon don't appear on the map, so you'll have to engage each Solrock you see. Shiny Solrock doesn't look too different from a normal one: its body is slightly redder and has blue pupils.
When you find a Shiny, you'll get that distinctive sparkle that will let you know you've found one.