Peshawar, Islamabad and Lahore is where you will find the US Embassy in Pakistan. These three locations both have the ability to ensure that you can apply for consular assistance or a new US passport while in Pakistan. You can also apply for a US visa in Pakistan and it would be best to seek the services of a lawyer in Pakistan for this task.
The Embassy of the US in Sri Lanka is in the city of Colombo and close to Mercantile Investment. If you wish to visit the US and are from Sri Lanka then you can apply for a tourist visa from the US embassy. If you are wanting to take your Sri Lankan wife back to the US you can apply for a US Fiancee Visa or if you are married you can also apply for a K3 visa or a CR1 visa while your wife is in Sri Lanka.