It's very common. In my experience, it's the Black Man who has always initiated and it must be done in the most discrete manner. They have a keen awareness of vulnerable whitebois and will seize an opportunity to use a submissive boi as long as it's on the down low. In the days of Craigslist it was a Black buffet but now that's moved onto other, less private, platforms that I do not use. So, my contacts have come from random social encounters, sometimes cultured from spending time where Black Men are likely to be found, sometimes out of the blue. Black Men can read a boi without us having to be in-his-face about our hunger and it's better if you are subtle.
Example: Some time back in a hotel elevator by myself away from home, a beautiful Black Man wearing a wedding ring got on and pushed a floor below mine. I'm not sissy at all but he read me anyway. Admired his radiance a fraction too long, I suspect. Standing back to me at the door a moment before he got off, he turned his head toward me and bluntly but quietly said, "you wanna suck me?". Naturally I was in his room and on my knees two minutes later with thick Black ass pushed into my grateful face. Key there was that he initiated in a private setting right before he was about to exit so no awkward moment if I didn't respond.
Social media (grindr, tinder, growlr, etc.) works for many. As jozxyt said, be as convenient as you are discrete. As personally fulfilling as it can be, it's all about catering to his need for full submission with discretion and convenience. For every King needing an obedient mouth there are legions of whitebois eager to take both knees.