There are a couple of acoustic bass guitars that "stand up" to acoustic "jams" as you call them. One is the Martin offering and the other is the Taylor. There are varying degrees of tone and volume in each of these, so I'd try to play as many of them as you can get your hands on. One Martin bass might be more desirable than another, so I'd be aware of that too.

Remember, bass is sometimes more effective when "felt" (even acoustic) and that you hear less of the instrument because you're behind it. Trust your bones and know the music you play. Try bringing a loud guitarist with you and a third "audience" member when you try them out.

And you can always approach a luthier and have one built. I played with a fellow in Kerrville who had a huge, redwood, 5 string custom built. It could sustain itself proudly beneath fiddles, multiple guitars and a crowd of singers and gawkers.