Do some quality link building from High PR web pages.

I think for getting good page rank you gave to take help from social site.

Quality links for PR 6-7 websites can certainly get you high PR.

May be this thread could also help you.

http://www.warriorforum.com/adsense-...page-rank.html

Link building to high ranking websites will do good. Social Bookmarking, Forum posting, blog commenting would do the trick. avoid black hat techniques.

"BUY" It's that simple.