There are plenty. They do not advertise open positions because that always results in a flood of applications that overwhelms their ability to scrutinize the applicants.

Find someone in the U.S. who is in the django market, and get to know them. (Google Plus, etc.) They can get you in touch with the right company (i.e., willing to help relocate, including visa issues) at the right time. You will probably have to do some contract work for U.S. companies first, however, so they can scope out whether its first going through the expense and hassle of relocating you.