I just remembered a friend of mine has a goldfish tank for her daughter. She is willing to give me some gravel and her old filter media. She changes it every month or 2 and I believe they are activated carbon cartridges. The tank is 2 years old her daughter won the fish at a fair. I asked her if they have ever been sick and she said no. I read that these types of goldfish can carry disease, so I am looking for advice on this. Thanks!
While the filter media and gravel may be worth pursing (I'm not familiar with the goldfish so can't say), don't bother with any used carbon filters. What about a local pet store with a nice established tank or a local fish club?
"Listen to some of these guys talk, and it's like they were born from their momma's belly with a fishkeeping encyclopedia in one hand and an API kit in the other" (unrevealed).