Don't stock up too much on tubing, as it's always been available in FIRST Choice and Freelin-Wade will sell at half-price to FRC teams.
As stated, the brass connectors are available at local hardware stores. The push-to-fit fittings are available through AndyMark in FIRST Choice as well.
Do not use the plastic household plumbing fittings like
this. They are not pressure rated. You can get plastic push-to-fit fittings on McMaster, Amazon, or a number or other suppliers that are pressure rated.