Answer:
Click on this link to the Fed's Interdistrict Check Manual page:
On the page is a drop-down list of all the check processing offices. You can click on any office in the list and you'll see, under the heading "General Information," a list of the Routing Transit Numbers assigned to that office. You'll note that it does not include any numbers beginning with "2" or "3." You should add "20" to the first two digits of each of the numbers listed to come up with a complete list.
As you know, the lists are in flux with the realignment of check processing districts.
First published on BankersOnline.com 10/03/05