I'm a little more than curious about a MFM partnership. I'm female and think I would be more fulfilled with 2 men.
My issue is finding 2 straight and poly men who are open to and comfortable with this arrangement. Is it REALLY that rare?

You're looking for actual people, not anonymous "M."
The best way to go about it is to start dating, letting guys you meet know that you are not open to an exclusive relationship. Many men will be fine with this, as many horny men just want casual relationships. They may not care who else you screw, as long as they are getting theirs.
The trick is to find men who are actually familiar with and into polyamory, as you see it and want to practice it. They need to understand that one can be in a committed, respectful, full and loving relationship, without being exclusive.
Modern polyamory is a new thing. It's based on female empowerment. For millennia, women have been seen as sluts if they have more than one male lover. We are pioneers. We need to help people understand what polyamory really is.
So, first you find one guy who understands poly. Then maybe along the way you'll find another guy who does too. These are 2 relationships--you and M1, then you and M2.
It's what is called a V. And you would be the hinge. Here is where things get complicated.
Both of these poly men may have other lovers as well. They may not want to be monogamous just with you. That's one pitfall to prescribing this form of relationship.
Next, they may or may not want to meet each other. If they do meet, they may or may not like each other. If they do like each other, they may or may not want to have 3way sex. If they do want to have 3way sex, they may or may not have issues with touching each other.
If you want to add in cohabitation, that's a whole other thing to work out.
So, there you go. This should get you started on your education.