Finding just the silencer may be a little difficult. Most of the time the silencer and expansion cha!mber are sold together. I have one pending sale, if it falls through I would sell both together. PM if interested..
Just email Arlan at his new shop LED Performance. Arlan@LedPerformanceEngines.com I just had them do a full custom system for my bike I'm sure he can help you with a silencer.
It wouldn't really be custom for a Blaster. Mine was a 1 off as my bike is a 1978 DT175 with a +4 240 kitted Blaster motor. Many other mods as well. My exhaust system cost $1500. He still builds Blaster pipes tho so they won't be any where near as much.