http://www.scrapmetalforum.com/forum.php Might be a better place to ask It is full of people that love to take apart components like that. I feel that if they is any silver it would only be plated with silver. Silver is to soft a metal to be practical for connecter it would deform when placed on the CRT. Keep in mind back when that part was invented silver was still being use in photography and far more expensive then it is today. The price of silver today is only $20.88 an ounce
http://www.jmbullion.com/silver/ I do not think there could be enough silver on those sockets to justify the amount of time it would take to extract them. I would just throw the ones you collected so far into your brass bin and cash out.