Revision 7f3f0f9d-c034-439c-9737-2671d40c2d90 - Code Golf Stack Exchange

## PowerShell v2+, 90 bytes

 for($a="0.";!($b=$a.IndexOf($args)+1)){for(;'1'*++$i-match'^(?!(..+)1円+$)..'){$a+=$i}}$b-2

Combines the logic of my [Find the number in the Champernowne constant](https://codegolf.stackexchange.com/a/66884/42963) answer, coupled with the prime generation method of my [Print the nth prime that contains n](https://codegolf.stackexchange.com/a/80446/42963) answer, then subtracts `2` to output the index appropriately (i.e., not counting the `0.` at the start).

Takes input as a string. Finds the `999` one in about seven seconds on my machine, but the `33308` one in quite a bit longer (*edit - I gave up after 90 minutes*). Should theoretically work for any value up to index `[Int32]::Maxvalue` aka `2147483647`, as that's the maximum length of .NET strings. Will likely run into memory issues long before that happens, however.