Any shop that sells Parker or SMC should have them....look up those names in your phone book. I have them on my wagon and dually. And have a bunch laying around in my garage cause my old jobs machinery is all Pneumatic and had boxes of them in the parts room.
They make "flat" silencers, "cone" silencers, Cone adjustables, and the white smc adjustables. the cone and flat brass silencers, the difference with those are the flats are slower than the cone shaped silencers.
I only have a few brass ones and they are only 1/2" I have 3 white SMC 3/8" silencers....they work/sound the same as the brass ones. And my dually/wagon just make a hissing sound when I set them down.
Why do you only want the brass ones? They work the same as the white SMC ones... Only reason I have brass on my dually is because they are shorter and the space my valves are in is small.
I had the white ones on my mazda and you can definately still hear it dump. I was going to try stuffing some cotton in them or something to try to make them silent...didn't exactly get a chance to do that though