Do you want a single tail, or a bull whip? Whips are like 12-15ft in length, and do require a great deal of skill (not to mention room) to play with.
Single tails can be as short as 3ft, though often are around 5ft or so length. That's a usable size to play indoors safely without having to get rid of everything in the room!
For more information on whips (as well as a local maker of them) check out
http://dallasdogsled.com/. Taipan is a great guy, and he'll happily show you how to play with a whip. He's been in the local scene for quite some time, and has been known to make single tails as well. If he's not currently making them, he'll tell you who is and where to get a good whip for a fair price. He can also tell you the same about bull whips if that's what you want.