Union end return ells

Samster

Ok so I have figured out what I have, it is a two pipe steam system with those union end return ells, on the outlets of each radiator, they look kind of like at 'T' but with the top capped off, they have a ball in them that acts as a check valve.

The problem is I am missing the cap for two of them and the ball in few more. I have been reading "The lost art of steam heating" it mentions them and how they work but it doesn't say what to do to replace them or to verifiy they are working??

Any body know where I can get parts or replacements?  The ones that are complete seem to be working fine still.

Or what to replace them with?

Any info would be greatly appreciated.

Samster