Assuming Gen 8 since Pokerus doesn't exist in Gen 9:
Wild Shiny: 1/4096
Wild Shiny w/Charm: 1/1365
Wild Pokerus encounter: 1/21845
Wild Uncommon Mark: 1/100
No charm Shiny Pokerus Uncommon Mark:
4,096 • 21,845 • 100 = 1/8,947,712,000
With charm:
1,365 • 21,845 • 100 = 1/2,981,842,500
For the record, the chance of finding a specific pattern of Spinda is 1/4,294,967,295.
MonkeyBusiness would not recommend.