had replaced veteran leaders with young, militant leaders

A concise list of non-profit organizations, by county, can be found at http://www.taxexemptworld.com/organizations/wisconsin-counties.asp

To find a list of non profit organizations, check online at the site Non Profit List or List of Non Profit Organizations. Try your local phone book to find a non profit near you.

Yes it is correct, but in text is should be written 'a thousand organizations'. Either is correct however:

We have a 1000 organizations on our mailing list.

We have a thousand organizations on our mailing list.

See: List of anti-war organizations.