I don't know where you could get the connector itself. I would recommend just cutting the Spruce harness short and tie into your own.
+1 on just splicing into your wiring. They recommend soldering the wires from the Spruce ones directly to the terminals on your GA jacks with the existing wires. I haven't done it yet either, but I have two harnesses sitting in my hangar waiting for warmer weather...
doesn't it wrankle a bit to pay $60 for a plug that should cost $5? I was hoping there was a digikey equivalent. I am sure Bose doesn't make these themselves. Or is it me? My Scots blood?
One more drawing from the Bose manual to help with connecting to existing jacks.