You can try refills at Officemax, etc.
Never ask for a replacement. Just be straightforward and say that you want your original cartidge to be refilled. You don't know where the replacement has been and you don't know how many times its been refilled.
After so many runs, you will end up having to buy a new cartridge, for efficiency. Printer manufacturers make a ton of money from ink, which costs less than what the American Blue/Red Cross offers blood for, on average expenses.
Avoid buying used ink cartridges on ebay. Some people learn the hard way.