Two places to obtain these:
look for SOC further down the page
I believe the first link is what you are looking for. Not sure if the second like is the same but it appears to be.
Note that both of these are "open", they continually pass air through them, there is no shutoff valve built in. You need to add an external shutoff valve (also available from the first link). And Kingston KMBVF Series Brass Mini Valve, 1/4" NPT Female looks like it will work.