Oxygen machines are hard to fine in my nearby area as there are very few medical equipment shops here. So the only way is to deal online or with the manufacturing company directly. I followed this way too.Some of the routinely used oxygen machines by a hospital or by a private practitioner are :

• Hyperbaric oxygen chamber - lots of uses of this chamber
• Pulse oximeter for routine blood gases pressure monitoring
• Oxygen concentrators
• Home oxygen machines
• Oxygen cylinders and more.

I found a nice site selling these oxygen machines and such other medical equipments at competitive rates with easy to use online shopping system - its DrMedicalEquipment.com. You can make online payment via secure checkout process and they will deliver the product to your address within few days. Many products are FFA approved including Sequal Eclipse, Inogen One Portable Oxygen Machine and more.
Hope you will find the site useful.