Appreciate the suggestion John... Digikey does indeed have a wide variety of speakers to choose from. I did a lot of exploring there and ended up looking at some of the rectangular / oval speakers, and ordered a few to try out:
CMS-402811-28SP, SC400308-1, and SC400608-1
I rigged up a little test to get power to the Cruise Commander and the Railsounds Commander boards so I could test each speaker against the one that came with the Railsounds Commander kit and sample the various sounds - chuffs, whistle, bell, crew / tower talk, etc. After doing so I was pretty surprised with how good all 3 of these speakers sounded, and to my ears each was at least as good as the speaker from the Railsounds Commander kit, and maybe even slightly better. And each was an improvement over the original speaker which didn't impress me much at all when I ran it a few times.
