I bought mine from a friend who sells home entertainment and car audio systems. Apparently DVD players for home theaters get dirty, too. I've also seen them in electronics superstores and office superstores that sell computer equipment. Google "drive cleaning disk." I thikn you'll find something
As an example of what these can do, a friend has an older Macbook Pro. It could read and write DVDs but any CD made the optical drive play dead. An Apple Authorized Service Provider (AASP) examined the computer and pronounced the optical drive dead as dirt, quoting a replacement cost of around US$150 for parts and labor.
I loaned this friend my cleaning disk, which I had bought for a DVD player connected to our TV, and he used it on the MacBook Pro. The drive was fully restored and, last time I checked, he was still using the computer with a 100% working optical drive.
For the cost, it's an inexpensive first step that often works and, if it doesn;t fix your computer drive, you have a gadget that can clean anything that plays CDs or DVDs. Very nice for automotive CD players in dusty environments.