We have been holding 2 clothing exchanges a year for the last 8 years. Each year we learn a little and add a little.
The resources for holding a clothing exchange fall into four main categories. Facilities, donations, wo/manpower, and planning. Basically you need someplace to do it. You need clothing to share and people to set up, organize clothes, and clean up. Also vitally important is someone who can pull all the details together and make sure the word gets out.