Canon Sales generally are the least expensive place to buy print heads from, especially those that use the CLI-8 and PGI-5 cartridges. the print head for my MP830 was significantly less expensive via Canon than anywhere else.
Currently, Canon is rationing print heads of at least one older model, such as my MP830, and probably more models. You can only get one at a time as of 10 days ago and Canon is keeping track of who buys in order to prevent aholes who purchase multiples and them reselling them on eBay (or wherever) for sizable profits. I asked if the devastation in Japan had anything to do with the rationing as was told no.
I looked at the business Mikling posted on, first on ResellersRatings.com and then on Google. I would rather go through Canon than them regardless of OSD's pricing. To each his own.
Lastly, your print head is toast for Pigment Black ink printing. It could be due to a malfunctioning logic board, but those errors usually give an error message.
Symmetric misfires like yours are not due to clogs -- unless your print head is one in a exceedingly large number that needs differential calculus and
pi to figure out. The most likely fix for you is a new print head (though there is a slight chance it is due to the logic board or another part). Given the functionality and ease of refilling, the price of a new print head is a small price to invest in reviving the printer.
If you don't care to try a new print head, sell the printer as is with full disclosure. You will be able to get some money back. (cueing ghwellsjr

)