Business recorder (www.brecorder.com) is a serious newspaper, which has a large target audience audience among the business community. Other than that, hook up with EPB (export promotion bureau). The EPB helps in bringing buyers and sellers together, both locally and overseas. If you are marketing in Pakistan, it will help you find buyers in Pakistan. If youre selling from Pakistan, it will help you find buyers overseas. Vice versa if youre buying, it will help you find sellers.
Other than that, you can contact the chambers of commerce in major cities. You will find a lot of helpful stuff at www.fpcci.com.pk.