Every Canon printer requires a certain type of Canon ink cartridge. The MP550 cartridge is for the MP500 series printer. Unless it is a refillable ink cartridge the actual cartridge has to be replaced once the ink runs out. If it is refillable then you can refill it once then you must get a new one or your printer could be damaged.
How can you find a Canon MP550 ink cartridge if you do not have internet access? This product can often be found at electronic stores throughout the country, so you should be able to go down to a local retailer and ask at the customer service counter. The people who work there should be able to tell you if they have the item.
If the ink that you need is for you canon mp550, then you should get the kind of ink that your printer requires. The best bet is that you get canon branded ink.
A great place to buy replacement ink cartridges is Amazon.com. They offer a wide variety of ink cartridges for nearly every printer on the market. It is okay to use refurbished ink cartridges, however it is preferred to buy new ones.