Thanks for your comments.

At present, I see two ways to do it.

Read each column in as a variant, and iterate through that instead of
constantly hitting the worksheet. This has a limit to how many cells I can do
at one time. Not sure what it is, but I've hit it in the past.

Add an extra column that checks to see if a value in a column is equal to
the value above it. Using INDIRECT, I can put a column number in a cell and
search over the same range for each column, looking for False.

"=AND(INDIRECT(CONCATENATE(""RC"" &
R1C),FALSE)=INDIRECT(CONCATENATE(""R[-1]C"" & R1C),FALSE))"

This formula looks at the top row of it's column to determine which column I
will test. After I find all the False's for a column, I change the number at
the top to look at a different column and search again for False's. It's not
as fast as I would like, about 5 seconds, as it takes a finite amount of time
to update the column when the top value changes. That's why I was hoping I
could use Find.

After I'm done, I delete the column.