{Collins} Mechanical Filter adapter

Good morning, I would like to purchase a Collins 353C31 adapter. This is the 3.1khz plug-in mechanical filter adapter for the 75A1. These may be scarcer than I realize so barring that possibility does any one have a schematic of this unit so I may build my own. 
Thanks and 73 Jerry K9GOZ
Sponsored by the Collins Collectors Association http://www.collinsradio.org
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