Actually there are quite a few airlines hiring. When you cut out the majors there are still 50 airlines in the US that hire flight attendants. In addition to the ones mentioned, you can add USA3000, Ryan, ATA, Alaska, Allegheny, etc.
You can find pretty good listing by signing onto PlaneJobs.com, or check out these job bulletin boards where I have posted past openings:
I will add this board to the websites I post openings as well.
Tim Kirkwood, Author
THE FLIGHT ATTENDANT JOB FINDER & CAREER GUIDE