The original question seems to have been asked back in 2010 but since it has been dug back up in the above two posts let me just add to the general knowledge. First, the ISPR will not disclose the nuclear warhead yield as it is an 'operational' information. If Pakistan armed forces term something as 'operational information' it means no discussion on the subject whatsoever. Secondly, only the top - the utmost top - officials at ISPR 'may' have the information on the subject. So, getting in touch with some random officials is not going to be helpful. In fact, people here dealing with opensource research & analysis on Pakistan's nuclear programme may have more knowledge on the subject than those officers.
The comprehensive information and knowledge on Pakistan's nuclear arsenal are of course with the Strategic Plans Division (SPD), the Secretariat of National Command Authority (NCA) - the formal Command & Control System of Pakistan. Within SPD, however, there seems to be an informal policy of 'one hand should not know what the other hand is doing.' Meaning, individuals and sub-organizations within SPD attend to tasks and routines assigned to them and they don't ask each other of their tasks, unless necessary. Asking random officials within SPD is also not going to get you information on warhead yields. That information is limited to - utmost top officials - only. I wouldn't be surprised if the DG SPD is the only person possessing the complete picture on the subject. He, of course, would be updating the prime minister and the service chiefs on the subject when required.