My iPod is stuffed with about 2 GB of old radio shows. There's a great site called RUSC.com where you can subscribe & download MP3 files of old shows. I subscribed for a month & downloaded as much as I could (for cheap, too). My fav show is Suspense & the remakes of Hollywood films with the big stars.
Anyhow, they do have some Robert Montgomery radio shows on there:
Khandi Tooth Caper, The (Suspense)
An hour of suspense with the distinguished actor/director Robert Montgomery as the host. In this episode the star is Howard Duff famous for his roll as Sam Spade Detective and as Spade he will appear in The Khandi Tooth Caper a Suspense play produced, directed and edited by William Spier.
Broadcast Date: 10th January 1948
Beau Brummel (Lux Radio Theater)
London 1820, Beau Brummel's fashionable house. Brummel discusses the events of the previous evening with his manservant. He is reminded that a note has been received from a certain party that the £3000 which he lost three nights ago is due to be paid that very day. A marriage to a rich lady of some standing would seem to be the answer.
Broadcast Date: 5th July 1937
Thing in the Window, The (Suspense)
You look out of your window at the apartments opposite and see a man sat in a chair facing the window. The next day you look out of the window again and the same man is sat in the same chair in exactly the same position. What do you do? Do you go across to the apartment block over the road and check it out for yourself. What if the apartment superintendent checks with the two spinster women living in that apartment only to find that there is no man in that apartment? You return to your own apartment only to find that the man is still sat in the chair - still in exactly the same position!
Broadcast Date: 19 December 1946
There's a more complete list of RM's radio shows over on the Earl of Hollywood web site.