Hello, do you remember the time when it was played? Or can you recall some vocals or part of the melody?
If it was a new/fresh show you may find it by typing 26-05-2012 into the search field at the top of the page or here.
If it was a replay of a previous aired show, you can either use the Advanced Search field and modify the options there or navigate yourself through this sub forum: http://www.ah.fm/forum/forumdisplay.php?178-Livesets. In both cases you should look out for posts that have been made around that day/time. Usually ppl do also comment on replays.
Regards, Squall.