Hi Thrums try carrotink.com. My cousin recommended them and also my sister buys from them for her business. She has high volume printing. She did say that one cartridge for nx4000 has lasted a long time, but another cartridge for a smaller printer in her business didn't last very long (6 months). I myself refill at Cost Co for $8. I live 150 miles from nearest Cost Co so I take 2 cartridges at a time to refill (one is my back-up). Good luck, Chris