dear Susan I'm a singer too.

Did I understand you to mean that no one plays the chords? They should be learned. The sheet music usually has this above the notation. Otherwise, they're not too hard to find.

Now, if they asked you to join them, then shouldn't they back off and let you be heard? When you are singing, then they play around with the chords, fiddlers using a long bowed note or notes, creating the movement of the chords, and the others too, then there's even dropping out (heaven forbid that they don't get to play for a little while- personally I find that space very refreshing!). What they do behind you shouldn't compete with the vocal. Unless you find some beautiful match, an instrumental tone that complements your own vocals. I know this is hard in a big band. Everyone wants to play.

Of course you can't use the words "back off"--how about..."let's create some space here" or here's another trick: don't try to compete, but sing normally, even a little light, then when they can't hear you, some sensitive soul will realize that something needs to be done...

Good luck