Every modern radial tire is speed-rated, and it is listed on the sidewall of the tire. a pic showing where it is located on the tire .
shows where to find those markings.
Here's a link to show what the speed designations mean
As far as getting tire rated for a higher speed, its just a matter of going to your local tire supplier, tirerack.com, discounttiredirect.com, etc. and seeing what they have available in the rating you want/need.