Staples (make sure to use your company account):
Printer Ink & Toner Cartridges | Staples
Office Depot:
Lexmark:
Lexmark Supplies | Lexmark United States
B&H Photo:
Printer Ink Cartridges & Printer Toners | Ink & Toners | B&H (bhphotovideo.com)
Amazon (our last choice, please make sure the ink is genuine):