An add-on to a previous post -
There’s a one-hour, 1943 Lux Radio Theatre production with Edward G. Robinson as Spade. Scroll down to number 173.
The 1946 Academy Award Theater production is only 30 minutes, but Bogart, Astor, and Lorre reprise their starring roles from the 1941 movie. It’s available on CD at Van Belkum and Yankee Clipper in two different old-time radio collections. There’s more Sam and Effie in “The Adventures of Sam Spade” with Howard Duff as the hard-smoking detective. No other big stars, but a fun half-hour program.