Unless you have a strong network in the US, developing for US clients is probably better suited as a long term goal.
Using Eastern European contractors doesn't have a clear and obvious upside for US companies. The main argument for outsourcing overseas has always been lower prices and good clients don't think that way.
Good clients want to work with people they know and when that doesn't happen they ask people they know for recommendations.
What I am saying is that you can put a lot of time, energy and money into trying to develop a US client base, but unless you are world famous there's not a good reason to choose you even if your work is good. There are a lot of good US developers, and a lot of other good developers outside the US.
Good luck.
