The Turner Classic Movie channel frequently plays William Powell films. I list times as they post on the site, but please check tcm.com for all updated times (all USA/Eastern):
6/12/08 The Thin Man 6:45am
6/12/08 Another Thin Man 8:30am
6/16/08 The Thin Man Goes Home 2:30pm
6/16/08 Libeled Lady 4:15pm
6/18/08 After the Thin Man 6:00pm
6/20/08 Double Harness 4:45am
6/23/08 The Kennel Murder Case 9:45pm
6/24/08 The Last of Mrs. Cheyney 2:15am
7/01/08 Reckless 5:30am
7/15/08 Evelyn Prentice 5:15am
7/16/08 Rendezvous 6:45am
7/29/08 Double Harness 1:00pm
7/29/08 The Thin Man 2:15pm
7/29/08 Love Crazy 4:00pm
9/04/08 Jewel Robbery 9:15pm
9/04/08 One Way Passage 10:30pm
9/22/08 One Way Passage 11:15pm
Brand spanking new! The Myrna Loy & William Powell DVD Collection includes “Manhattan Melodramaâ€, “Double Weddingâ€, “Evelyn Prenticeâ€, “I Love You Againâ€, “Love Crazyâ€, plus the radio adaptation of “Love Crazy†by William Powell, cartoons and shorts.
Also available on DVD: The Complete Thin Man Collection, The Great Ziegfeld, How to Marry a Millionaire, Libeled Lady, Life With Father, Kennel Murder Case, Man of the World (as part of the Carole Lombard Glamour Collection), Mister Roberts, My Man Godfrey
For a full filmography, see www.imdb.com
Many of his early silent films are feared lost. As for the talkies, some are available on VHS only (most are out-of-print). Both Amazon.com and eBay are great places to look for used titles, as well as the occasional bootleg.
William Powell: The Life and Films by Roger Bryant
Gentleman: The William Powell Story by Charles Francisco (out of print)
The Complete Films of William Powell by Lawrence J. Quirk (out of print)