Acutally, in a number of years of dancing, I have worn a tail suit for competition and for shows, but never at a social occasion. I've worn a tuxedo at a few formal parties, but tails would have been overdressed.
For social dancing, I originally bought a used tuxedo from a rental shop. The disadvantage of a regular tuxedo is that the jacket is designed for people who keep their arms at their sides. In particular, when you take dance position, the shoulder pads tend to rise up break the top line. But since in social situations nobody is judging your top line, it's not too bad. It is just important to fit the jacket so that it does not pull when you take dance position.
For competition use, people typically have a tail suit custom made, or look for one used. If you know anyone who competes in your area, they might know of local sources for used dancewear. For social use, it might be possible to alter a regular tux jacket,