There are links to all 26 NPC sorority websites via
http://www.npcwomen.org . Not all are obvious - for example, Kappa Alpha Theta is thetahq.org, not kappaalphatheta.org.
The NPHC groups are found at
http://www.nphc.org .
Other groups, such as Latina, Asian-American, Multicultural and local can most likely be found by a campus or web search engine.