The WGBH website has a list of programs which originally aired on PBS and have been released on DVD with optional descriptive narration tracks and captioning. All but a few can be purchased by following the links to the product page on Amazon.com. The remaining discs listed can be purchased directly from PBS at the toll-free number listed under the disc title.
Description of many PBS programs is funded by a grant to the Media Access Group from the U.S. Department of Education. WGBH's Media Access Group is an Amazon Associate, which means that when you click through their site to purchase movies or TV shows on DVD from Amazon, they receive a small portion (4%) of the revenue. As a nonprofit organization addressing media access barriers of all kinds, they are grateful for the financial support you can provide through your purchases.
Click this link to see the list of PBS Programs on DVD with DVS.