Unfortunately Bruno Walter is not my guy, and particularly on Richard Strauss and therefore I would not help you. However, I would suggest you to find a different, more productive venue to research performances after those “just heard” experiences.
Bruno Walter has a large community of fanatic followers and they publish very detail lists of Bruno’s performances and his official and unofficial discography. There is a Bruno Walter Society that pressed many of his “left” performances, and some of them were quite good. When you hit the Bruno Walter communities with thier listings I would suggest to pay attention to the Japanese based sites: they sometimes published some performances that were not available on West.
Also, Scott, be advised that sometime classical radio stations can broadcast the recordings that never were publicly available - they have own archives and have access to the recourse that you do not! Here is where you have to hit the collectors who record those live broadcasts of the broadcasts retranslations. BTW, some radio stations still keep the tapes of the Live Broadcast recordings and sometime run them directly to air. The quality of sound in there is wonderful (if you have a good FM section and a good antenna) and here is where you have to have your Nack ready… :-)
Anyhow, welcome to the world of the Real Audio.
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche