I was in the same situation. The company I was working with shut down. I submitted the experience letters that I had with me. You can write a letter explaining what happened with the company. Mention the company name, address, Managing director's name, your relieving date and year of shutdown clearly on the letter. CHC knows that such things happen and if your company was a legitimate then CHC should be convinced.
Check out my thread: http://www.canadavisa.com/canada-immigration-discussion-board/urgent-help-needed-letter-from-employer-but-company-shut-down-t18301.0.html