Just take the certs to your brokers office,
And surrender them after filing out some forms, and they'll sell them right there on the spot and deposit the funds in your account, or write you a check.
If you have to mail them in because you aren't near your Broker's office, it's much harder but doable...That's why I use Scottrade for my cash account, because there's one in Tulsa which is only an hour and a half drive from me.