I'm a little bit confused. You're not moving to the US, you're just interested in getting something checked out with a US doctor while you're there visiting? Or, you're moving to the US and interested in getting coverage right away?
If it's the first one, I would be very surprised if a US insurance company would cover you for something like that. I think in that instance, you may have to pay out of pocket. If it's something totally rare then maybe you could get a research MD to see you pro bono, but I think that would be near impossible.