You can go to Netsol.com and look up domain names. I wouldn't use anyone else. The reason is that Network Solution is the sole authority for domain names and always has been. Others can resell names and for some reason can offer them for less. But, I have had experiences when I looked up domain names from some of these companies, found one I liked, then when I tried to purchase the name, it was unavailable and had been purchased by the company I was using to search.
Since this is for organizations, you can use the .org name instead of .com. These are generally more available. When you get a name, copyright it. That will protect you in case someone tries to steal your name.
If you want ideas, look at the one I created for my chapter.
http://www.ricebelt.org.
Good luck...