This will probably be helpful to you for finding the tainted area.

TerraMap is a world viewer that allows you to highlight blocks for easy location finding.

TEdit is a Terraria world editor which will allow you to not only view the world, but also make changes (including simply removing the tainted area right away).

If you're dead-set against creating multiple hellevators in your world, the only realistic way to locate the missing Corruption/Crimson/Hallow is to examine the world in a third-party viewing tool. It's tedious to clean up if you want to make the world look nice again. Unfortunately, this method is very expensive and leaves your world scarred.

Then, use a clentaminator to purify the world. One guaranteed way of clearing out a tainted area is to dig a 'hellevator' (a 2-wide tunnel straight down to the underworld) every screen width apart. If needed here is the world download if there are no efficient tips and tricks that can work so that I may at least get some help finding the round about area the crimson and hallow is. I am also trying to stay away from destroying the world since it is my main world and would prefer not to look over the entire world as it is a large world which means that by the time I found it, it probably would have spread more already.

If anyone has any tips or tricks for finding this last bit I would gladly try them because every solution I have found online does not help me in the slightest. I have tried using Tedit to find the coordinates of the last blocks but that did not work and I have also tried the MoreTerraria world viewer to find those last blocks but it keeps giving me an error when I try to draw a world. I have been working on getting my main Terraria world to 100% pure(No Hallow Crimson Or Corruption) and I managed to get the world to 1% Hallow and 1% Crimson but can not find those last 1%s.

How to use terraria map viewer