The charity organization Habitat for Humanity has opened a number of thrift stores nationwide where companies and individuals can donate furniture to be sold to the public. The profits made from selling donated furniture go to Habitat's housing projects.
The Salvation Army charity receives donation of furniture (including office furniture) from many sources. Buying furniture from the Salvation Army ensures that money spent will go to help those in financial distress.
Check local Goodwill thrift stores for office furniture. These stores often have unique older pieces just waiting for a new home. A portion of the purchase price will go to the many charitable causes championed by Goodwill.
Beverly Farm accepts donations of new and gently used office furniture to be sold at company warehouses with the proceeds going to benefit programs such as the Equestrian Therapy Program.
Look for local hospice charities such as the Browse and Buy in New Philadelphia, Ohio. Many hospice organizations sell donated furniture to fund programs.