How can I get MotoGP tickets for Portugal??

I am going to Europe in Sept. and would love to get tickets for the Portugal races, how do I go about getting tickets or checking on availability? Thanks

I searched for you and found that they were available off this website... http://www.gpt.at/en_home.htm you can select english if it's in german...then go to moto gp and scroll down to find the Portuguese grand prix. They have tickets available for several grandstands... I hope that helped!