http://mooneyspace.com/search/?type=all&q=Oxygen+equipment
you will find so many answers depending on how you intend to fly your plane. Some people will have a preference of mask vs canulas...
The connecting hardware may be specific to your plane.
Scott and Mountain high aviation are brand names that people around here have used.
There are some altitude restrictions to the type of mask or canula you intend to use.
This is PP advice. Not to be confused with a CFI...
Best regard,
-a-