Hi, I've blackmailed dozens of people (consensual blackmail) and some of my "victims" have been with me and under my complete control for many years (see my albums for more of my slave Emma, who I often like to show off here on Kinktalk). Over the years I've blackmailed both males and females, and had many stumbles and missteps as I figured out how to explore this kink in a realistic and sustainable way, without taking the edge/fun out of it.
While I'm not personally interested in blackmailing males, I'll offer some thoughts that may help you.
1. Think hard about what you are really looking for. Do you wan't to be exposed or blackmailed? People often confuse the two.
If exposure is your kink, you want the material to get out there. You don't actually want to be forced into obedience, you want to disobey and to be exposed and you see blackmail as a part of the journey of being exposed. While in a true blackmail situation you will do anything to prevent the material from being released. In a blackmail situation you want to obey, or be made to obey, and the blackmail material is the insurance that guarantees you have no choice.
2. Think about if you are looking for a partnership/dynamic with a firm but supportive blackmailer who will encourage you to open up and give them more over time (the style I prefer), or are you looking for an adversarial relationship where you are constantly testing and pushing back so that your blackmailer must force/threaten you constantly to keep you in obedience. Many people enjoy this as well. Try to find a blackmailer who shares your ideal dynamic here, as they are quite different.
3. Keep in mind that single males in their 20's who want to be blackmailed are a dime a dozen (really!). I get messages literally every day from single males who want to be blackmailed. So think hard about what you have to offer someone.
As a blackmailer, I am inundated with people who have decided they want to be blackmailed and focus entirely on their own wants and act as if they are entitled to be blackmailed by me and have their fantasies fulfilled. Just because you are ready to and looking to be blackmailed, doesn't mean anyone actually wants to blackmail you. Because it's such a huge decision that takes incredible courage, this can be very confusing for an aspiring victim who has finally decided they are emotionally ready to go through with it, and then can't find anyone who actually wants to do it with them.
It doesn't mean you won't find someone, but keep in mind that it is a lot less appealing to someone like me to blackmail someone who is single, hasn't established themselves, and has few attachments and little to lose.
4. Decide up front if financial blackmail is your thing. If so, then lucky you, there are plenty of money Dommes/Doms who will take you. If not, be prepared for a more challenging search. Keep in mind that once you are blackmailed, you have no choice and no "out", so try to read between the lines with whoever you are talking to to see if they are looking for money.
5. When you do find someone who you thing may be a good fit, enjoy it and take your time. Don't give up your information/material up front. The process of slowly revealing the material is probably the most exciting part, so milk it for all it's worth. I've taken up to several months of slowly getting to know a victim before finally hitting that "point of no return" (usually in the form of the victim giving up their real name/address, humiliating full-face pic/video, etc. ). If the blackmailer is demanding the material up front before starting the blackmail, my advice is to move on.
6. I strongly encourage you to find someone who has actually blackmailed someone before (and can show you proof). I can tell you from experience that the first time a blackmailer gets full blackmail power over another person it is an incredibly intense feeling of power. They will want to test that power. If you are the first person they blackmail, you may be in for some intense days as they push harder and harder to see how far they can really push someone, and how it feels. If they have blackmailed someone before, they will certainly have personalized pics/videos/etc that could prove it. Pay attention to the language they use when talking about their previous victims. Do they sound protective of them? resentful? or do they sound like they are they just making shit up?
I don't want to discourage you. I believe that blackmail is the closest you can realistically come to true slavery. The relationship between a blackmailer and their victim can be one of the strongest and most intimate bonds I've ever experienced. Nothing brings you closer to someone than the power to destroy them completely, or be destroyed by them completely. The risks are huge, but so is the reward when it works.
Good luck with your search!