Shiny Golem in Pokemon GO isn't actually to hard to achieve. It's the first step that's the hardest. First you'll need to catch a shiny Geodude , which will take a bit of luck and some appropriate Spotlight Hours to help game the RNG. Shiny Geodude is gold in its standard form and reddish orange in its Alolan Form.
A Pokémon Spotlight Hour is set for Tuesday, August 25, from 6 to 7 pm local time. During the hour, there will be an increased number of Geodude appearing in the wild, and you’ll earn double Stardust from catching Pokémon.
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— Leek Duck (NYC) (@LeekDuck) August 24, 2020
Shiny Golem Pokemon GO: How to Catch
From there it will take 25 candies to evolve the Pokemon into Graveler. Candies received catching both Alolan and standard form Geodude work for both.
The next step is a little more difficult or incredibly easy depending on whether or not you have a friend that also plays. Graveler can be evolved into Golem both by using 100 Geodude candies and by simply trading it to another player. If you have a friend you trust to give the Pokemon back to you once the trade is finished you can have a shiny Golem the second your Geodude evolves into Graveler.
If not you'll just have to build up a stock of candies from catching the Geodude line in the wild. Pinap Berries can significantly speed up this process.