It is pretty rare. You can pay to do it or join a ball room dance club, if you can find one.
Most larger communities have ballrooms where ballroom dancing is enjoyed by movers and shakers - just like you! Find one, and have a ball! [pun intended]
The military still has formal balls with ball room dancing.
There are Mardi Gras Balls (giggle) every year.
Depends on where you are, with whom you are acquainted, and the musical tastes of all involved.
That have them in most major cities. Ball room dance clubs, and of course the politicians in DC host them all the time. :)
Where I live there are lost of salsa batchata dance nights