2 Answers

I dont have a Canon printer but if I did have a particular model I'd pull on some plastic until I found it.

Word to the wise, a few years ago I bought a canon S900.. Great printer..  The cartridges were like 12 bucks apiece. It uses 6. 

I looked online and I found a place that would sell Canon 'compatible' for 4.99 each. So i bought them.

After using this crap, I noticed that the colors would not last, a couple weeks and the colors looked yellow.  Then the worst happened, my print head got clogged.  I did everything to clean it, i went to printer forums, they are real printer geeks, they told me that i was screwed and i would need a new printer head.  I finally took it in to canon service, my printer was out of warranty but I didn't know what else to do.  After about a week, they called me and said come pick it up.. When i got there i was expecting the worst as they told me a new printer head was like 90 bucks. 

The technician told me 'no-charge' but he also told me what happened, it was that cheap ink, Canon inks are specially formulated for high heat, these 'compatibles' are not and they bake onto the printhead, there's a few thousand 'nozzles' there very tiny, they will clog and ruin if you use anything other than canon..  i was fortunate, I still use this printer today and its great but I will only put canon ink in it. -- where to buy??  How about the same place you bought the printer?  Canon is a popular brand and you should find the inks at any retailer authorized to sell canon products, and that's most of them..