This size is also available in grade N50 with black nickel plating as part number D21B.
I drilled a 1/8" hole in Evergreen .060" strip styrene, CA'ed the disc magnet in so it was flush on both sides, then used a razor saw to cut tapered long and short ends, then rounded them off. I glued the long end into the hose made of very flexible surgical rubber in a vertical orientation (see below.)
Because of the disc magnet's polarity, you need to make sure that your gladhands at one end of a car are mounted up-side-down relative to the other end, and that all your cars are done the same way. This means that you'll always have to couple "A" ends to "B" ends (which I usually do anyway.) Once you've coupled up, push the hoses towards each other and they'll snap together. The magnets are very strong and hold well, but when you uncouple, they shear off and disconnect very realistically.
In my first attempt to make the airhoses connect with magnets, I used thinner ones that I got from the same place - 1/8" dia. x 1/32" thick - glued directly to the gladhand casting. I encountered two problems with this approach however: the first was getting the magnetic polarity right - sometimes they would repel each other or connect on the sides rather than face to face; and second, even when they did connect correctly, the thinner magnets weren't strong enough to stay connected, they kept coming apart.
I suppose I could have used the thicker discs, but that makes the gladhands look distorted and I'd still have the polarity problem anyway. That's why I came up with the "omni-directional" scratch-built ones as shown above. They may not look as good as the stock castings, but they work great and do look good when connected.