You've hit the nail on the head there, it is difficult to find a submissive willing to understand or make the effort to live this way.
Online opens up a whole new world of exploration for BDSM. And to me it's a seemingly easy way to fall into a comfort zone where expectations and commitments can be easily obtained or discarded. No harm no foul to certain people.
That's the way I see it anyway.
I think that there are few people who really understand the realities of a poly relationship. It sounds romantic, ideal and a wonderful way to live when reading about it, but the work and effort to live it becomes a slap in the face, when one has to start living it.
I think this lifestyle sometimes falls under the category of cool. Much like a submissive who declares she is bisexual because Dominants like that.
Polyamory is intriguing and submissives would love to be able to say that they can live this life and there are no issues at all.
Then I think that because of all the information that is thrown around about finding the one, being the best submissive, being strong and independent get misconstrued altogether.
A submissive doesn't understand that while they are important in a poly environment, they are not the one and only submissive in the relationship.
It's a difficult process at best to adjust to and one that requires a lot of soul searching, hard work and commitment.
I for one would prefer to share in the way that you describe, however I have yet to experience it to the fullest so I am still unsure as to whether or not this particular lifestyle is to my liking.
I do understand what is involved and am prepared to do the work and make the effort.
It is probably rare that you will find a submissive who does understand the concept and is willing to work at starting a relationship with you both.
That isn't to say that they aren't out there. I do believe you can meet someone online, but the searching is the hardest part to it.