I got a note from Dr. Robin Wood - hurray for Google! - with whom I began a conversation on Hanley points back in 1999 when I started dealing books online. Although he doesn't see himself as a collector, he is a fan and has gone to quite some length to dig up uncatalogued Hanley material. Here's his partial "Not in Gibbs" list:
(1) Reviews in the North London newspaper The Recorder. An article 9/6/50 on Hanley by Emrys Jones: "Great Novelist Reviews the New Novels". Thereafter more or less weekly book reviews by Hanley until 5/4/52, when Emrys Jones takes over again. Dr. Wood did not make copies, or record details, as the reviews were generally prosaic and generally not of well known authors.
(2) Stage Plays
1972 Leave Us Alone --10 performances in London ( Cont. Brit. Dramatists 1972). According to Guernsey in The Best Plays of the Year 1972-3. Confirmation of the performances from Hanley's son Liam.
1973-74 Say Nothing for five months, at the Finnish National Theatre (Harington 23). Additional documentation, including reviews.
(3) BBC SOUND RECORDINGS (National sound archives):
Winter Journey LP 24037 a play 29/1/58
The Ocean T28269 novel adapted 4/5/58
One Way Only T32636 a play 1/12/67
A Dream Journey T37964 adapted from his novel 30/11/74
Another World T49571 a play by James Hanley 20/5/80.
I'd really like to assemble as complete a list of Hanley material as possible, so if you've found this site and got notes on a couple of Hanley oddities, do send them in.