Theres lots of personals sites. collarme.com alt.com and fetlife.com and many more.

They often let you organize by state and some even by city or metro area. when I did this for curiosity fetlife had 256 people in my area and collarme had even more.

The real question is once you start looking at these sites is how do you narrow down who you want to start corresponding with!!!!

Not to mention that if you get familier with local clubs etc lots of places have bdsm events for singles!