Any electronic store such as the ones mentioned, or Frys, should have something. What is your application? If it is something like HVAC then a 370 VAC might be a better number. 1.414 X 240 = 339 volts!
But if the application calls for 370, it is available I am sure. In most applications, there is no downside to using a capactor with a higher max. voltage rating.