Do you live in Sweden? Är du svensk? May I ask why you specifically want to ordain in the United States?
The two most obvious places I assume would be: and .
Maybe it could also be worth to check this one out: They seem to have some co-operation with Ven. U Dhammajiva of Nissarana Vanaya, which I think should make them worthwhile to at least have a look at. If it actually would be a suitable place to ordain, I can not tell.
Regarding the whole visa-issue, I would suggest that you take contact with an american embassy or similar. This could be the tricky thing with ordaining in a non-buddhist country. It is indeed quite unlikely that they will have special bhikkhu/meditation-visas...
But as it is said: If there's a will, there's a way...
I wish you the best of luck with your noble aspirations,
The customs and rituals of people with kilesas are numerous beyond description, unlike the ways of Dhamma which are always constant and unalterable.
- Ãcariya Maha Boowa Ñāṇasampanno