It's not on my computer either. I was told to go to sprint.com/chat. I did that and actually found the chat site. However, I have been chatting with myself for over an hour. No help for me at all but perhaps you will have better luck.
The Chat icon currently displays during normal operational hours only when chat agents are available:
If agents are not available to chat, or it is after regular operational hours, then the Chat icon will not display on those pages.