Hello AudiDriver,
Welcome to the HP Forums!
I understand you would like to replace your printheads on the Officejet 8500. I will provide a HP website called the HP Parts Store. You can purchase a printhead here or you can order by phone: 1-800-227-8164Monday-Friday 7:00am-7:00pm CST, Saturday 8:00am a 7:00pm CST.
If you have any further questions, please let me know.