A notarized self-declaration, along with a letter of explanation outlining all the efforts taken in vain to procure said reference letters, will also serve the purpose as a last resort. Because handing over such a letter to CIC clearly indicates to them that you're sticking your neck out and are willing to risk being found out for any possible misrepresentation on the work experience front and are fully aware that, in such a case, your application can be refused on those grounds. That will work in your favor if all your experience was indeed genuine and you couldn't procure reference letter for some reason or the other.
Of course, always ensure that you provide CIC with enough material (websites, physical address, contact details, key personnel etc) to help them perform adequate background checks in such cases. If there exist NO trace of the organisation at all, send a letter of explanation and hope for the best.