I have compiled a list of sources for the elements that are available to the amateur chemist. Oxygen will be discussed here.
Oxygen is a colorless, odorless gas. It supports combustion and is necessary to life. It is regenerated by all plants. Oxygen reacts with most elements. Oxides are widespread as minerals. Oxygen is the most abundant element in the earth's crust.
In element form: Electrolysis of water makes oxygen gas. Catalytic decomposition of hydrogen peroxide produces oxygen. Oxygen is used in welding.
In compound form: Silicon dioxide has oxygen in it. Water and hydrogen peroxide do, too.
Here is my sample of oxygen gas. It was from a welding gas cylinder. I originally had oxygen from H2O2 decomposition, but the tube was not clear enough to see through. Any apparent coloration is the result of a dirty test tube.