You just have to find the sub that is perfect for you.
Which means, you have to decide exactly what you are looking for in your D/s relationship...kinky sex only? A service sub? A little girl to your Daddy dom?
Then, you have to make sure you are the perfect Dom for the type of relationship you want. Being the Dominant in a Ds relationship doesn't mean you get to sit back and just issue an order every now and then, you have to be actively involved in the growth and health of the relationship. You have to be willing to put the hard work into training and you have to have your life under control before you can expect to take control of someone else's life as well.
You should get involved in your local lifestyle community, so you can see how real life D/s relationships work. This will also get your name and face out there in front of potential submissives who might be looking. Join Fetlife, even though it is not so much a dating site as it is a social network, or try OKCupid, which does have a lot of kinky people on it, all looking for relationships! Learn about BDSM, the activities you enjoy, go to seminars or demos...but DON'T go around calling yourself Master this or Dom that unless you can really walk the talk, submissives are not stupid, nor are they desperate, and you will get seen through as a fake unless you can back up your claims about yourself with action.
Finally, understand that a lot of the BDSM porn that exists is unrealistic...every sub you meet is not going to be flawlessly beautiful, hungry for your cock and willing to do anything and everything you desire at the drop of a hat. Know the personality you like and be willing to overlook things like age, weight, hair color, etc. because that subby who's breasts might not be as big as you like might also be the most loyal, best submissive you have ever owned and you will never know it.
Good luck !!