Searching for & downloading older radio programmes
I'm aware of the technical difficulties BBC has been experiencing, and I'm glad to see that things are getting better --I've successfully downloaded two recent episodes of Gardeners' Question Time.

I'd like to download older episodes, and I reckon that if the BBC GQT page lists a given programme as "over a year left to listen", I should be able to use get_iplayer to search for and then download it.

I've tried using get_iplayer with various search options, but so far can only get these two recent episodes to show up in the results.

I thought I'd read somewhere that I could search by PID, and I believe the PID is listed in the URL of that epidode's web page, but now I can't find that section of FAQ/Wiki/Guide.

I feel like I'm almost there but not quite --any suggestions, pointers to a FAQ or Guide section that I should go study, etc. would be very much appreciated.
Huh! This seemed to work:

get_iplayer --type=radio --pid <pid number>

I thought this would have just searched, but it downloaded the programme. Works for me : -)
If the programme episode is not available via the iPlayer or iPlayer Radio sites, you can't search for it since it won't be in the listings used by get_iplayer. For old episodes available only through a series web site, use the PID as mosaica instructed, or just use
get_iplayer --type radio <episode URL>