You can get the 5-cylinder powerplant that the Focus RS500 uses in the States in the form of a Volvo C-30. I have not heard of anyone pushing a new ST up past 300bhp. You cannot send your car to Ford to get the 5 cylinder engine. The $1,500 Hennessey HPE300 optional dealer installed upgrade will get you around 300whp.
Original Focus RS (Europe) was based on the WRC Focus, used the same 2.0 Zetec engine that was factory turbocharged. Many people in the U.S. have gotten a hold of everything needed to convert a U.S. Focus into an RS - it is not cheap. Most of these one-off Focus RS here in the States cost more than $20,000 just to convert.
The Focus ST (worldwide) is 262hp
The Focus RS500 (Europe) is 350hp
The 2015 Focus RS should be coming to the United States and it will look like a widebody ST
