How can I get ink sacs?

So for a while, I've wanted black wool to make banners. Tons of people have banners in their cells, and I tried a few designs in my creative world that I like. I thought I was ready, and then I realized, how can i get ink sacs? Any help is greatly appreciated!
1: they weren't obtained from fishing, in the early days alchemy used to give them when breaking lapis.
2: you can get them from the shop in the sp world