Honestly, I don't think that you can just go and get them refilled. Your best bet would be to just go buy new ink cartridges for your printer. It's probably cheaper anyway.
The best place to buy ink cartridges online is on amazon. They sell them in bulk, and they also sell discounted cartridges that have been refilled and work just as well as new ones.
There are a number of retailers that sell good quality refilled ink cartridges. I would recommend Re-Inks (online) and Cartridge World. You can also buy kits to do it yourself.
The cheapest ink you can buy is refilled cartridges on websites such as amazon. They work just as well as new ones and are half the price, although most printers will not recognize that the cartridge is full.
Buying refill kits for ink cartridges is much more economical than purchasing brand new cartridges. It is even possible to send your old cartridges out and have them refilled and sent back.
My first choice to buy Ic51 ink cartridges online would be amazon.com. Office Max and Office Depot have good deals for ink cartridges as well. www.colortonerexpert.com/LC51Inks sells them as well.
Ink cartridges Canon are expensive, and each printer takes numerous cartridges. Buying replacement ink is sometimes more expensive than the printer was when purchased new. You can buy refilled ink cartridges to save money. Most printing jobs will look great with refilled ink, but if you print a lot of photos, you may want to try refilled ink on a few test photos to check the quality.
If you are certain that your cartridges are full, then I would not be concerned about it. If you can, I would buy a brand now cartridge and see if it recognizes it.
A good cheaper alternative to ink cartridges are to use "refurbished" ones that are empty manufacturer's cartridges that have been refilled by a third party. Companies such as Cartridge World offer them for sale for 50% - 75% off the regular price you would pay for a brand new one from the manufacturer.
Refilled ink cartridges can be a significant money saver depending on the printing needs of your home or business. Although you can buy the refill kit and do it yourself, this can be messy and takes practice. If you touch the contacts or over-fill the cartridge, it may be ruined. Find a local vendor who specializes in refilling cartridges and bring your empty ones when you go, because many have a trade-in discount.
I do not recommend you buy and try to use refilled cartridges.
You can buy Canon ink cartridges in many different places. Amazon usually has very competitive prices, but you could also look at refilled cartridges on ink sites such as Simplyink for cheaper prices.
Brother laser printer cartridges are special because they can be refilled by the user rather than taken to an expensive ink store or the user having to buy a new one.