For Spinda, one would never have enough boxes for all the combinations, and it would take you 5000 years to find every one.
It takes about 40 seconds to get into a battle, catch a pokemon with full health and a critical capture and go back to the overworld. Assuming you caught Spinda before, ran into a different variation EVERY time and got a critical capture on every spinda it would take 171798691840 seconds to capture every variety. That's 2863311530 minutes and 35 seconds. That's 47721858 hours and 50 minutes. That's 1988410 days, 18 hours and 50 minutes. That's 5444 motherfucking YEARS and 32 days.
That's not taking shininess into account, so double that number assuming you also had each variation caught and then it's shiny variation straight after.