I would take your Excel list of numbers and make it a one line list that has a ";" in between each number and copy it to the Search area of Windchill. You must have Index searching turned off though. I think that there is a limit to the number of characters in one search though. You can have "*" in the search criteria as well. It is the Keyword search.
It would look like this:
Then you could export the list to Excel from Windchill and do some comparisons within Excel.