I'm seeing a great deal of discussion on here about swingers clubs where white women have access to black men. While I think this is a great idea, I find that when I am out in public I see an awful lot of white women and girls already with black men. Or if I don't see the black men I see white women pushing black bi-racial babies around in strollers. It seems to me that the women know where to find the black guys
It seems to me that you are not merely asking for a black bull, but you are asking for a Black father for a baby who will not interfere with the parenting of the baby. And you are asking for them to be guaranteed disease free. I don't blame you for the second stipulation, but there is no absolute guarantee except perhaps locking him up for the length of the relationship with multiple STD tests over the course of a year. Good luck finding someone who will meet that demand!
However the ramifications, the baby will grow up without knowing his or her biological ancestry. This includes the possibility of various genetic issues that include many issues that will affect his lifestyle choices lifelong, including diabetes, sickle cell anemia, cancer, heart disease, and alcoholism. As a medical professional, I wish people would think that part of the issue through before they turn their fantasy into reality.
Socially, you will be criticized for your choice by family, friends, and colleagues as it will be completely obvious that your wife chose to have sex with someone else outside your marriage. An issue that I do not think enough people think about is that the baby may have trouble finding a role model for their racial identity. There has been a lot of discussion about this issue around adopted children that you can look up, but we have seen it played out in our own families. You will need to be intentional about helping them to find that racial identity and affirming who they are and it is not easy.
Finally in answer to your question, unfortunately there are far too many men willing to father a baby without responsibility. This site will have many volunteers, but you can send your wife into a nightclub or adult bookstore alone and she will walk out with three men offering to spend the night with her. There are a dozen other websites from Yahoo backpages to Adult friend finder to any heterosexual porn site. Finding a bull will not be your problem.