Sadly, there is no 'Dom shop' where you can order your perfect custom built Dom to be delivered directly to your door. I know, because I looked for one. Clearly there is a gap in the market there, but in the meantime, what is the solution? There is no tried and tested method. The most important thing is that you know what you are looking for which hopefully means when you do stumble across it, you will be better able to identify it/him as right for you.
I met my Dom on a site for kinky erotic amateur writers. Sadly, it no longer exists, but neither of us were there expecting to find a partner. Yet, that is exactly what did happen. So my advice is to always be open to meeting someone in the oddest or most unexpected of places. That might be a website for some other, unrelated hobby, or in my case a slightly related hobby or might even be at work, through a friend, or even in the supermarket. I know it sounds like a Hollywood movie, but it does happen.
Prior to meeting my current partner, I also met a Dom on a vanilla dating site. A bit like the above option, I was not there expecting to met a kinky dominant man, but that is exactly what I found. I am not saying vanilla dating sites are full of them, but they are there. It is just a case of finding them. Make sure you write your profile in such a way as to make it clear the kind of man you are looking for, and also when you are looking through matching profiles be sure to read between the lines. Often, people leave clues or hints if they are kinky, but also remember that not every knows they are kinky. It is perfectly possible for you to help someone discover their kink just as you have. The key is finding someone who clicks with you.
There are also sites dedicated to kinky folk and I would encourage you to try these. In particular, I recommend that you check out Fetlife. It is a huge site and it can be a little complicated to find your way around, but it is the place to find out about your local kink community. In my opinion, it is the place to go where you are most likely to meet a potential Dom. Try searching for you local town, county, etc., and join the local groups listed. If there is a local munch, go to that and start to get to know people. From that community you will start to build real life friends and connections within the kink community. There is every chance that it will be within that community you will find the partner you desire.