"Yes, the Laser Jet 9050 is compatible with Hewett-Packard computers. There are many different printers in this series of printers, each with different specifications."
The HP 9050dn is a laserjet printer, so it requires a toner cartridge. The HP 43X LaserJet Toner Cartridge will work with that particular model. The toner cartridge can be purchased directly from HP.
"There are many different online retailers that sell the Laserjet 9050dn, which include, PC Rush, Printer Stop, The Printer Pros, Quick Ship Toner and many other retailers."
The LaserJet 9050DN is a printer manufactured by the Hewlett-Packard company. Refer to the company website for info on their products. Their corporate headquarters is located at 3000 Hanover Street in Palo Alto, California. If neither of those seem a viable option, a technician or salesperson at a store that specializes in computers and/or electronics should be knowledgeable on the subject.